add contributing.md

Author: tomglvng

README.md

@@ -161,3 +161,9 @@ The support of this client is made in best effort by our Akeneo team.
 
 If you find a bug or want to submit an improvement, don't hesitate to raise an issue on Github.
 Also, you can ask questions and discuss about the PHP client with the community in the [Slack User Group](https://akeneopim-ug.slack.com/messages/web-api/).
+
+## Contributing
+
+As this PHP client is an open-source project, all contributions are very welcome!
+
+For more information, please consult [the contributing section](contributing.md)

contributing.md

@@ -0,0 +1,19 @@
+# Contributing
+
+Want to do your bit for our PHP client? All contributions are warmly welcomed!
+
+## Contribution process
+
+First and foremost, please accept and sign our [Contributor License Agreement](https://www.akeneo.com/contributor-license-agreement/).
+
+And then, do your magic :
+* Fork our repository
+* Create a branch (choose a descriptive name)
+* Work on your own code (don't forget to add necessessaries tests)
+* Commit your branch and submit a pull request to our projet
+
+At this moment, the ball is in our court: we will check your PR and add comments or suggestions if needed.
+
+When everything is ok, we merge your work.
+
+Congratulations, you are officially a contributor to our dear PHP client!