Add/update GOVERNANCE.md, CODE-OF-CONDUCT.md and CONTRIBUTING.md

CODE-OF-CONDUCT.md

@@ -0,0 +1,3 @@
+## Community Code of Conduct
+
+gRPC follows the [CNCF Code of Conduct](https://github.com/cncf/foundation/blob/master/code-of-conduct.md).

CONTRIBUTING.md

@@ -1,6 +1,9 @@
 # How to contribute
 
-We definitely welcome patches and contributions to grpc-swift! 
+We definitely welcome patches and contributions to grpc-swift! Please read the gRPC
+organization's [governance rules](https://github.com/grpc/grpc-community/blob/master/governance.md)
+and [contribution guidelines](https://github.com/grpc/grpc-community/blob/master/CONTRIBUTING.md) before proceeding.
+
 Here are some guidelines and information about how to participate.
 
 ## Getting started

GOVERNANCE.md

@@ -0,0 +1 @@
+This repository is governed by the gRPC organization's [governance rules](https://github.com/grpc/grpc-community/blob/master/governance.md).