message: update repo layout
diff: @@ -81,6 +81,8 @@ currently implemented but that is the plan moving forward.)
  `Envoy::Extensions::ListenerFilters` namespace.
  * [filters/network/](/source/extensions/filters/network): L4 network filters which use the
  `Envoy::Extensions::NetworkFilters` namespace.
  + * [grpc_credentials/](/source/extensions/grpc_credentials): Custom gRPC credentials which use the
  + `Envoy::Extensions::GrpcCredentials` namespace.
  * [health_checker/](/source/extensions/health_checker): Custom health checkers which use the
  `Envoy::Extensions::HealthCheckers` namespace.
  * [resolvers/](/source/extensions/resolvers): Network address resolvers which use the
  