Add instructions for using MySQL

[deso2021]

data is stored in /db/badgerdb by default? how to enable store in postgres

[tijno]

i have a postgres run setup here

https://github.com/tijno/bitclout-run

check the progres branch of that repo

[maebeam]

Use the --postgres-uri flag or POSTGRES_URI environment variable. FYI Postgres is deprecated in favor of MySQL

[deso2021]

The data in the pg_balances table looks incomplete. After the synchronization is completed, sum is 5786567.577867775，should be 10.8M ?

select sum(balance_nanos)/1000000000 from pg_balances;

[tijno]

@deso2021 there's a remaining issue with negative balances @maebeam is aware off