docs: Added contribution guide

Fixes pact-foundation#483

CONTRIBUTING.md

@@ -0,0 +1,86 @@
+Contributing to PactNet
+=======================
+
+Raising Issues
+--------------
+
+Please don't raise issues for general queries (e.g. usage queries) and instead check the [Pact Docs] site or ask on the [Pact Foundation Slack].
+
+Before raising any issues, please make as much effort as you can to rule out issues in your own environment as much as possible.
+For example, if you are using a self-hosted Pact Broker instance and PactNet is failing to connect, please ensure things like the
+authentication token and SSL certificate are valid.
+
+If you are sure that the issye is with PactNet then please raise an issue, including as many of the following details as you can:
+
+- PactNet version
+- Your operating system and version
+- .Net version
+- Log output
+- Steps to reproduce and/or a repository link which reproduces the issue
+- Expected outcome
+- Actual outcome
+
+Due to the way that PactNet works, often issues that are found are not in PactNet itself but instead in the [pact-reference]
+native FFI libraries. If this is the case then an upstream issue will be raised in the FFI repository and PactNet will have to
+wait until the fix is available in a new FFI release.
+
+Raising Pull Requests
+---------------------
+
+For new contributors it is recommended that you start a discussion with a core maintainer prior to raising a PR. This
+is for your own benefit so that you don't waste time implementing changes which don't align with the project in general
+or will require significant changes afterwards.
+
+The best way to achieve this is to open an issue detailing:
+
+- The problem you see at the moment
+- The solution you propose to fix this problem (e.g. adding a new feature, refactoring an existing API, etc)
+- Any downsides you can foresee as a result of this change
+
+If an issue already exists for the change you wish to contribute, please comment on the existing issue.
+
+After raising your PR, a core maintainer will review your change and may request/suggest changes. Please take the
+feedback in the spirit intended so that the PR can be merged as quickly as possible whilst still meeting established
+conventions within the project such as architecture, code style, test style/coverage and API evolution.
+
+In particular it is much harder to make any changes which involve a breaking change, so please set expectations accordingly
+if your change requires a new major version. A large and/or potentially disruptive change should typically take the form of
+an RFC issue.
+
+A good example of an RFC issue preceding a major change is [PR 457].
+
+Building PactNet
+----------------
+
+In order to build PactNet you must first download the native Rust FFI libraries. You can pull the current supported
+version by executing the script in Bash (or Git Bash on Windows):
+
+```bash
+build/download-native-libs.sh
+```
+
+Alternatively you can download a particular FFI version from the [pact-referece] releases or build your own version
+locally, and then copy the artifacts into the folders:
+
+```
+build/
+    linux/
+        x86_64/
+            libpact_ffi.so
+    osx/
+        aarch64-apple-darwin/
+            libpact_ffi.dylib
+        x86_64/
+            libpact_ffi.dylib
+    windows/
+        x86_64/
+            pact_ffi.dll
+```
+
+After the native libraries are in the expected places then the solution can be built in your IDE or on the command
+line using `dotnet build` as normal.
+
+[pact-reference]: https://github.com/pact-foundation/pact-reference/releases
+[Pact Docs]: https://docs.pact.io/
+[Pact Foundation Slack]: https://pact-foundation.slack.com/
+[PR 457]: https://github.com/pact-foundation/pact-net/issues/457