contributing: Add branching how-to (#2963)

* contributing: Add branching how-to

* Add draft of branching itself

* Clean up commands

* Add creation of branch using web GUI

* Mention PR priority

* Wording

Co-authored-by: Veronica Andreo <[email protected]>

* Add note about recording the commit hash

Co-authored-by: Markus Neteler <[email protected]>

* markdownlint fix

* note down commit hash

* Add where website needs to be updated

Co-authored-by: Markus Neteler <[email protected]>

* Add notes from 8.4 branching

* Extent example version searches

* Spelling fixes, wording improvements

* Link to command line

* Apply most of the suggestions from code review

Co-authored-by: Veronica Andreo <[email protected]>
Co-authored-by: Markus Neteler <[email protected]>

* Chnage the title for addons update

---------

Co-authored-by: Veronica Andreo <[email protected]>
Co-authored-by: Markus Neteler <[email protected]>
Co-authored-by: Markus Neteler <[email protected]>
Co-authored-by: Edouard Choinière <[email protected]>

doc/development/branching_how-to.md

@@ -0,0 +1,142 @@
+# Branching How-To
+
+## Assumptions
+
+Given the creation of a new release branch will typically happen right
+before RC1 of a new release series, please see assumptions in the
+`howto_release.md` document.
+
+## Create a New Branch
+
+Given how the branch protection rules are set up and work,
+you need to bypass protection against merge commits on branches.
+(We don't want any new merge commits. However, there are merge commits
+from the past and they prevent the creation of a new branch when the rules are
+applied.)
+To bypass, go to _Settings > Rules > Rulesets > Rules for release branches_.
+Press _Add bypass_ and add the team or user who is creating the branch.
+
+Use GitHub web interface to create a new branch:
+
+1. Go to _branches_.
+2. Copy the name of one of the existing branches.
+3. Click _New branch_.
+4. Paste the name of the existing branch.
+5. Modify the name.
+6. Click _Create branch_.
+
+As an alternative to creation in GitHub, you can
+[create a new branch using command line](#create-in-command-line).
+
+Note down the latest commit hash on the branch to record it in the
+[release history overview](https://grass.osgeo.org/about/history/releases/).
+The instructions for updating the website come later in the procedure.
+
+Remove the bypass in _Settings_.
+
+## Check the Version
+
+```bash
+git fetch upstream
+git switch releasebranch_8_4
+```
+
+## Increase Version on the main Branch
+
+The version number needs to be increased on the main branch.
+
+```bash
+git switch main
+git fetch upstream
+git rebase upstream/main
+```
+
+Update the version in the source code (use `minor` or `major`):
+
+```bash
+./utils/update_version.py minor
+```
+
+If you are using a clone you use for building GRASS GIS,
+clean up (`make distclean`) your GRASS GIS build to remove
+the now outdated generated version numbers.
+(You don't need to build GRASS GIS if you have a fresh clone.)
+
+Search for all other mentions of the last few versions to see
+if they need to be updated, for example:
+
+```bash
+grep --exclude-dir=.git -IrnE "[^0-9^a-z]8[\._][0-9][^0-9]"
+grep --exclude-dir=.git -IrnE "grass8.?[0-9]"
+```
+
+After the check and update, commit
+
+```bash
+git switch -c update-version
+git add -p
+./utils/update_version.py suggest
+git commit -m "version: ..."
+git push
+```
+
+Create a PR and review and merge it as soon as possible to avoid having
+the wrong version on the branch in case other PRs need to be merged.
+
+## Server Updates
+
+On grass.osgeo.org (grasslxd), new version directories need to be created:
+
+```bash
+cd /var/www/code_and_data/
+VER=grass85
+mkdir -p ${VER}/manuals \
+                ${VER}/source/snapshot \
+                ${VER}/binary/mswindows/native \
+                ${VER}/binary/linux/snapshot
+```
+
+## Updates of grass-addon Repo
+
+* Add new branch into
+[`.github/workflows/ci.yml`](https://github.com/OSGeo/grass-addons/blob/grass8/.github/workflows/ci.yml).
+
+## Website Updates
+
+Add the branch creation to the release history (use the commit hash you saved earlier):
+
+<https://github.com/OSGeo/grass-website/blob/master/content/about/history/releases.md>
+
+## Additional Notes
+
+### Making Changes in General
+
+If you make changes, commit them:
+
+```bash
+git commit -m "version: ..."
+git push
+```
+
+(You can directly push to release branches.)
+
+### Create in Command Line
+
+Get the latest main branch:
+
+```bash
+git switch main
+git fetch upstream
+git rebase upstream/main
+```
+
+Create the branch:
+
+```bash
+git switch -c releasebranch_8_4
+```
+
+Push the version to the upstream repo:
+
+```bash
+git push upstream