https://www.youtube.com/watch?v=o8Fn9BgqoQM
first time : npm install --save express npm install --save socket.io sudo npm install -g nodemon
next time : npm install
anytime : nodemon server
- don't send message to oneself
- create a room
- automatically add someone to a room
- being able to accept or refuse to be added to a room
- what to do with message not received ?