Update CONTRIBUTING.md

CONTRIBUTING.md

@@ -10,7 +10,9 @@ github version of Faiss with the internal state.
 
 ## Pull Requests
 
-We welcome pull requests that add significant value to Faiss. 
+We welcome pull requests that add significant value to Faiss. If you plan to do
+a major development and contribute it back to Faiss, please contact us first before
+putting too much effort into it.
 
 1. Fork the repo and create your branch from `master`.
 2. If you've added code that should be tested, add tests.
@@ -39,14 +41,13 @@ disclosure of security bugs. In those cases, please go through the process
 outlined on that page and do not file a public issue.
 
 ## Coding Style  
+
 * 4 spaces for indentation rather than tabs
 * 80 character line length
-* C++03 for the main Faiss
-
+* C++03 for the main Faiss, C++11 for the GPU part
 
 ## License
+
 By contributing to Faiss, you agree that your contributions will be licensed
 under the LICENSE file in the root directory of this source tree.
 
-
-