Figure out if qiita_websocket is still in use and document its messages

[antgonza]

Currently, I'm not sure if qiita_websocket is still on use or left behind by mistake. Thus, it will be good to figure out if it's still used and if it is document what's exactly doing - if not, delete it.

The original source:

A comment on what 'hello' means might be good. Right now it reads like a magic number.

Originally posted by @charles-cowart in #3177 (comment)