Add a symlink to ./gitter-cli somewhere in your path, then run
Use k or arrow-up to go up in the chat board.
Use j or arrow-down to go on down in the chat board.
When focusing on the screen, press i for writing mode.
Use ESC to toggle between the screen and the input box.
When focusing on the input box, press ctrl-s to send the message.
For more information, see the gitter-cli package on npmjs.com.