Update documentation site to show grpc example tutorial (kubernetes-sigs#2277)

* Update mkdocs.yml

Forgot to add grpc-example to mkdocs so it shows up on the static site

* Update mkdocs.yml

Author: brianannis

mkdocs.yml

@@ -32,6 +32,7 @@ nav:
           - SSL Redirect: guide/tasks/ssl_redirect.md
   - Examples:
     - EchoServer: examples/echo_server.md
+    - gRPCServer: examples/grpc_server.md