First cut for updating HACKING.md with submodule documentation
First cut for updating HACKING.md with submodule documentation

Solinea/goldstone-server,slashk/goldstone-server,slashk/goldstone-server,slashk/goldstone-server,Solinea/goldstone-server,Solinea/goldstone-server,slashk/goldstone-server,Solinea/goldstone-server,Solinea/goldstone-server,slashk/goldstone-server