Improve dependency updating process documentation (#49)

.github/DEPENDENCIES.md

@@ -0,0 +1,48 @@
+# Updating dependencies
+
+## Dependabot
+
+We use [GitHub Dependabot](https://docs.github.com/en/github/administering-a-repository/keeping-your-dependencies-updated-automatically) 
+([bought by GitHub in 2019](https://dependabot.com/blog/hello-github/) and now 
+[baked into GitHub](https://github.blog/2020-06-01-keep-all-your-packages-up-to-date-with-dependabot/)) 
+to manage our dependencies.
+
+Whenever possible we let Dependabot update our dependencies automatically (by 
+[automatically creating a PR](https://docs.github.com/en/github/administering-a-repository/managing-pull-requests-for-dependency-updates#about-github-dependabot-pull-requests)
+for us to merge).
+
+Dependabot will 
+[automatically update non-Docker dependencies in our GitHub Actions](https://github.blog/2020-06-25-dependabot-now-updates-your-actions-workflows/).
+
+### Workaround for other dependencies
+
+For our other dependencies which cannot be updated automatically by Dependabot, we employ a bit of a hack.  
+We have a [`dependabot_hack.yml`](workflows/dependabot_hack.yml) GitHub Action which triggers a Dependabot PR when these other dependencies have a new version to update to.  This GitHub Action is set to never actually run; it exists just so that Dependabot can do its thing.  The `dependabot_hack.yml` documents where in our codebase that we then need to **update to the new version manually** (we then **add this manual update as another commit to the PR that Dependabot creates**).  NB we are able to use this hack to **manage _any_ dependency that uses 
+[GitHub releases](https://docs.github.com/en/github/administering-a-repository/about-releases)** - we are not limited to just dependencies which are themselves GitHub Actions (this is because Dependabot doesn't care
+whether the dependencies are valid GitHub Actions, it just parses the file and updates any versions that are
+managed through GitHub releases).
+
+We could in theory automate this entirely (by e.g. having a GitHub Action that is triggered by Dependabot PRs,
+which updates the version in the requisite files and then adds the change in a new commit to the Dependabot PR),
+but that would be overkill for now.
+
+Eventually as Dependabot adds more features we may be able to remove this workaround.
+
+
+## Dockerfile dependencies
+
+We have [pinned the linux dependencies in the devcontainer Dockerfile](https://github.com/agilepathway/hoverfly-github-action/pull/46/files), but there is no mechanism to automatically update them, currently.  It looks like [it's on Dependabot's roadmap](https://github.com/dependabot/dependabot-core/issues/2129#issuecomment-511552345), so we have reminders every 6 months to 
+1. update the dependencies manually
+2. see if Dependabot now offer this functionality
+
+### Updating the Dockerfile dependencies manually
+
+1. Temporarily unpin the versions (i.e. remove `=<version>` from each package in the Dockerfile)
+2. Execute the Dockerfile (e.g. if it's a remote container Dockerfile build the remote container)
+3. Run `apt-cache policy <package>` for each package, to see the version installed
+4. Pin all the versions, replacing any old versions with new ones
+
+
+## Ubuntu version
+
+[Ubuntu releases annually in April](https://wiki.ubuntu.com/Releases).  In 2020 the GitHub Actions team [supported the new version by mid June](https://github.com/actions/virtual-environments/issues/228#issuecomment-644065532), so we have an annual reminder for 1st July each year to see if we can upgrade.  We can find out [here](https://docs.github.com/en/actions/reference/virtual-environments-for-github-hosted-runners#supported-runners-and-hardware-resources).  When we do upgrade to the new version it involves e.g. for 2021, simply replacing every case of `ubuntu-20.04` with `ubuntu-21.04`.

.github/workflows/dependabot_hack.yml

@@ -1,4 +1,5 @@
 ---
+# See ../DEPENDENCIES.md#workaround-for-other-dependencies
 name: Dependabot hack
 on:  # yamllint disable-line rule:truthy
   push:

CONTRIBUTING.md

@@ -24,30 +24,8 @@ The [tests](.github/workflows/tests.yml) are [end-to-end black box tests](http:/
 
 There is no need for a separate language for the tests - as we are running the actual GitHub Action we are able to use the [GitHub Action workflow syntax](https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions), which gives us what we need (e.g. [expressions](https://docs.github.com/en/actions/reference/context-and-expression-syntax-for-github-actions#about-contexts-and-expressions)) to write clean tests.
 
-
 ## Updating dependencies
 
-We use [GitHub Dependabot](https://docs.github.com/en/github/administering-a-repository/keeping-your-dependencies-updated-automatically) 
-([bought by GitHub in 2019](https://dependabot.com/blog/hello-github/) and now 
-[baked into GitHub](https://github.blog/2020-06-01-keep-all-your-packages-up-to-date-with-dependabot/)) 
-to manage our dependencies.
-
-Whenever possible, we let Dependabot update our dependencies automatically (by 
-[automatically creating a PR](https://docs.github.com/en/github/administering-a-repository/managing-pull-requests-for-dependency-updates#about-github-dependabot-pull-requests)
-for us to merge).
-
-Dependabot will 
-[automatically update non-Docker dependencies in our GitHub Actions](https://github.blog/2020-06-25-dependabot-now-updates-your-actions-workflows/).
-
-For our other dependencies which cannot be updated automatically by Dependabot, we employ a bit of a hack.  
-We have a [`dependabot_hack.yml`](.github/workflows/dependabot_hack.yml) GitHub Action which triggers a Dependabot PR when these other dependencies have a new version to update to.  This GitHub Action is set to never actually run; it exists just so that Dependabot can do its thing.  The `dependabot_hack.yml` documents where in our codebase that we then need to **update to the new version manually** (we then **add this manual update as another commit to the PR that Dependabot creates**).  NB we are able to use this hack to **manage _any_ dependency that uses 
-[GitHub releases](https://docs.github.com/en/github/administering-a-repository/about-releases)** - we are not limited to just dependencies which are themselves GitHub Actions (this is because Dependabot doesn't care
-whether the dependencies are valid GitHub Actions, it just parses the file and updates any versions that are
-managed through GitHub releases).
-
-We could in theory automate this entirely (by e.g. having a GitHub Action that is triggered by Dependabot PRs,
-which updates the version in the requisite files and then adds the change in a new commit to the Dependabot PR),
-but that would be overkill for now.
+See the [DEPENDENCIES.md](.github/DEPENDENCIES.md)
 
-Eventually as Dependabot adds more features we may be able to remove this workaround.
 

README.md

@@ -141,3 +141,8 @@ The project is [open source](https://opensource.guide/how-to-contribute/) and al
 * [How to report a bug or suggest a new feature](CONTRIBUTING.md#how-to-report-a-bug-or-suggest-a-new-feature)
 
 * [How to make a contribution](CONTRIBUTING.md#how-to-make-a-contribution)
+
+
+## Updating dependencies
+
+See the [DEPENDENCIES.md](.github/DEPENDENCIES.md)