Add note about G Suite account requirement
Add note about G Suite account requirement

Fixes #8
googleworkspace/hangouts-chat-samples,gsuitedevs/hangouts-chat-samples,gsuitedevs/hangouts-chat-samples,gsuitedevs/hangouts-chat-samples,googleworkspace/hangouts-chat-samples,googleworkspace/hangouts-chat-samples,googleworkspace/hangouts-chat-samples,gsuitedevs/hangouts-chat-samples