Docs on Fixing Postgres Default Value Mismatches Is Incorrect

Sometimes you'll write a model file that has a default attr like default=FALSE and get constant no-op migration suggestions because persistent is expecting your model definition to be default=false.

In the Quasi module docs(https://hackage-content.haskell.org/package/persistent-2.16.0.0/docs/Database-Persist-Quasi.html), there is a little blurb about using \d+ in psql to get the proper value to put in default= to make these go away.

But this is not always accurate, apparently psql does a little bit of cleanup when rendering the defaults. The real way is to mimic persistent's query(https://github.com/yesodweb/persistent/blob/9723907352a9ab98f2384c44f3c47e13ffa81af7/persistent-postgresql/Database/Persist/Postgresql.hs#L794-L809) and pull the value from there:

SELECT 
  column_default
FROM 
  information_schema.columns
WHERE
  table_name='YOUR_TABLE_NAME'
AND
  column_name='YOUR_COLUMN_NAME'

One example is psql showing a default of now() + '120 days'::interval while persistent expects an attr of default="(now() + '120 days'::interval)".

Would be nice to mention this other query in the persistent docs.

Start with the Database-Persist-Quasi documentation and compare its \d+ guidance with the query shown from persistent-postgresql/Database/Persist/Postgresql.hs. Update the documentation to mention querying information_schema.columns and retain the default-value example so readers know what correct guidance looks like.