[CHANGE] Added contributing guide

Author: RouL

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+# Contributing code
+
+This repository is a collection of dev container Features managed by [Markus Zhang].
+This repository will **only accept improvements and
+bug fixes** for the [current set of maintained Features].
+
+If you're looking to create a new Feature, then we encourage adding it to a
+separate repository of your control. The [devcontainers/feature-starter]
+repository has more guidance on self authoring Features.
+
+Once you've self authored the Features and if you'd like to share them with
+the community, then I'd recommend [adding it to the index].
+
+If you've identified an issue and you want to fix it, here's how you can get
+started:
+
+1. Fork the repo
+2. Open the repo in your editor
+3. Add your changes to your workspace
+4. Add additional tests to your workspace if neccessary
+5. Test your changes using `bin/test <feature name>` to make sure everything still works
+6. Bump the version of the feature you changed according to [semver]
+7. Commit & push your changes
+8. Open a PR to get your changes merged
+
+[Markus Zhang]: https://github.com/RouL
+[current set of maintained Features]: https://github.com/RouL/devcontainer-features/tree/main/src
+[devcontainers/feature-starter]: https://github.com/devcontainers/feature-starter#readme
+[adding it to the index]: https://github.com/devcontainers/feature-starter#adding-features-to-the-index
+[semver]: https://semver.org/