Write oAuth documentation

To be faster, it can be written in markdown that we can then render in the documentation page using react-markdown.

## Routes (+parameters)
- `/authorize` 
- `/oauth/token`
- `/oauth/prello/login`


## Scopes:
- `boards:read`
- `boards:write`
- `users.profile:read`
- `users.profile:write`
- `teams:read`
- `teams:write`
