Document process for fetching and formatting user and reserves data

[defispartan]

Add a guide to the README explaining the process used on the Aave frontend to fetch and format pool data using the UiPoolDataProvider contract and formatReserves / formatUserSummaryData helper functions.

Add UiPoolDataProvider contract code and addresses to the GitBook docs.

[defispartan]

TO-DO:

Complete examples with GraphQL for V2 and V3
Create a separate repo with a minimum viable implementation of fetching and formatting protocol data via helper contracts