Mention gRPC port in docs.
Mention gRPC port in docs.

Closes #144.

brocaar/lora-app-server,jcampanell-cablelabs/lora-app-server,jcampanell-cablelabs/lora-app-server,brocaar/lora-app-server,jcampanell-cablelabs/lora-app-server,jcampanell-cablelabs/lora-app-server,brocaar/lora-app-server,brocaar/lora-app-server