[FAB-3340] fix broken link to contributing doc

Fix [FAB-3340] by changing link to point to the new location.

[ci-skip]

Change-Id: I772424dd2fff2e7f2e3a086dce7a959050c2b06d
Signed-off-by: Arnaud J Le Hors <[email protected]>

Author: lehors

README.md

@@ -28,7 +28,7 @@ information on getting started using and developing with the fabric, SDK and cha
 ## Contributing
 
 We welcome contributions to the Hyperledger Project in many forms. There’s always plenty to do!
-Full details of how to contribute to this project are documented [here](http://hyperledger-fabric.readthedocs.io/en/latest/CONTRIBUTING/).
+Check [the documentation on how to contribute to this project](http://hyperledger-fabric.readthedocs.io/en/latest/CONTRIBUTING.html) for the full details.
 
 ## Community