Any interest in adding README for `grpc-tools`?

### Is your feature request related to a problem? Please describe.
I find the general gRPC ecosystem to be a bit tricky sometimes for a beginner such as myself to find out all the pieces needed to get things up and running.

It took a while before realizing the value of `grpc-tools`, and it would have been helpful to know what its use case was earlier on in my technical implementation of gRPC

### Describe the solution you'd like
I'd be willing to open a PR that introduces a README in https://github.com/grpc/grpc-node/tree/master/packages/grpc-tools, if I get a green light from project maintainers

I'd mainly like to document `grpc_tools_node_protoc` and `grpc_tools_node_protoc_plugin`, and why + how they are used within a gRPC node based project

In doing so, any useful resources or feedback ahead of time that could help me provide useful documentation in my PR is welcome.