message: grpc: note about -Werror
diff: @@ -101,3 +101,5 @@ error while loading shared libraries: libgrpc++.so.1: cannot open shared object
  ```
  Make sure to apply the patch 0001-Makefile-fix-wrong-SHARED-version-suffix.patch before building gRPC.
  +
  +If the gRPC build fails because of warnings, you need to remove all `-Werror` flags in the gRPC `Makefile`.
  