Document gRPC and common classpath conflicts troubleshooting

For ALPN error, refer to [gRPC troubleshooting guide](https://github.com/grpc/grpc-java/blob/master/SECURITY.md#troubleshooting).

Add additional documentation for Guava and Protobuf related errors, and examples to shade.