Create an intro document for common queries and use cases

[bsamuels453]

I’ve received a few questions recently from users who want to query the subgraph for a certain type of data, but aren’t sure how to do it because they aren’t familiar with graphql or our schema.

It might be nice to have a USAGE.md document that covers:

1. How to open a graph protocol playground session to send test queries
2. Some example queries that users can plug in to the graph playground app
3. Make sure there’s a note about how graph protocol doesn’t have eip-55 support

Some potential queries:

1. View the last 30 days worth of VaultDayData for a given vault
2. View all deposits/withdrawal events for a given user
3. View the past 10 harvests for a given vault
4. View the profits a given user has earned on their deposit