Write docs

[pkamenarsky]

I.e. see https://github.com/pkamenarsky/concur-replica/issues/36. Needs to cover:

• Basic setup, custom JS, CSS, etc
• Cool examples, i.e. replicated/reactive state across browser tabs
• Explain how common idioms are represented in Concur, i.e. button with upload indicator
• Compare to other frameworks? Something like ui-zoo, similar to frp-zoo?
• ...

[seagreen]

This would definitely be cool.

One idea for a place to start would be to put a simple multiplayer game in the examples. Snake is a classic for this.