Add README for the Node diretory.
Add README for the Node diretory.

googleworkspace/hangouts-chat-samples,gsuitedevs/hangouts-chat-samples,googleworkspace/hangouts-chat-samples,googleworkspace/hangouts-chat-samples,googleworkspace/hangouts-chat-samples,gsuitedevs/hangouts-chat-samples,gsuitedevs/hangouts-chat-samples,gsuitedevs/hangouts-chat-samples