[Docs] Staking on Human App

[Dzeranov]

Description
Create a document describing required changes for Human App/Reputation Oracle to implement staking requirement on Human App

Context

1. Jobs discovery should be unavailable unless user has staked on either CEX or staking contract (list of supported exchanges will be defined later).
2. Users should be able to securely store their read-only api keys for CEX (need to think whether it's needed to store more than 1 exchange)
3. Extra rewards for users who staked more than X amount
4. Staking requirement should be 'pluggable' (so we could enable/disable it at any time without changing the codebase)