Update README.md

Update contribution doc

README.md

@@ -4,3 +4,9 @@ The Asset-Importer-Lib Documentation repository.
 Current build status: [![Documentation Status](https://readthedocs.org/projects/assimp-docs/badge/?version=latest)](https://assimp-docs.readthedocs.io/en/latest/?badge=latest)
 
 [Latest version from master](https://assimp-docs.readthedocs.io/en/latest/)
+
+## How to contribute
+- Clone from this repository 
+- Prepare a branch with changes in.
+- Create a pull-request
+- The pull-request will be reviewed and merged afterwards. We will add your name to the list of contributors.