[org] Clean up & document SingaporeJS Github repos

@ongmin

(converted from Erik's card on the project board)

There are many repos in our org that I don't have any idea about, I think we should clean them up and document about what's left.

Some actionable items I suggest:

Remove deprecated Gitter-related stuffs if we decide to permanently to Telegram
Reduce to properly 2-3 repos:
- This repo for talk.js
- Probably singaporejs.github.io for our website and other things
- (Optional) organisers repo for internal stuffs (although I think we can use singaporejs repo for it

To do? (get all votes then we move forwards with it)

Provide feedback