[Documentation] Improving Relay documentation

I'll write this issue as a way to tracking some points that I think that could be cool to have documentation about. Any contribution on this would be really help.

My intention here is improve how we consult this doc and turn more friendly to new users.

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## Documentation

- [ ] Improve organization of the notes

## Setup

- [ ] Setup with Koa / Express / Others...
- [ ] Setup Relay with other frameworks
- [ ] Explain about Network Layer
- [ ] Initial setup
- [ ] Implementation with other languages

## Examples

- [ ] NextJS example
- [ ] TypeScript example
- [ ] defer and other directives examples
- [ ] GraphQL Helix example