Add 'Contributing' section

README.md

@@ -67,6 +67,18 @@ $ ./deploy.sh --vagrant services SINGLE_SERVICE  # deploy SINGLE_SERVICE Docker
 Note that the `--vagrant` flag should be the first argument when using
 the script.
 
+## Contributing
+
+If you want to contribute, you can fork the repository and submit a pull
+request. We use a pre-commit hook for linting the YAML files before
+every commit, so please use that. To initialize pre-commit, you need to
+have Python and GNU make installed. Then, just run the following shell
+command:
+
+```console
+$ make init
+```
+
 ## Nice tools
 
 - [J2Live](https://j2live.ttl255.com/): A live Jinja2 parser, nice to