Merge pull request #204 from matyo91/fix/contributing

fix(contributing): Fix contribution documentation

Author: soyuka

CONTRIBUTING.md

@@ -27,6 +27,7 @@ To install the source version of the API Platform Client Generator in your proje
 ```console
 $ git clone [email protected]:api-platform/client-generator.git
 $ cd client-generator
+$ yarn install
 $ yarn watch
 ```