I add my comments to the commit message that contain the schema changes. If you seriously add a comment like 'required first name of user' you are wasting everyone's time.
last_name | character varying(50) | ... | required first name of user
Documentation that conflicts with the DDL makes for an easy code review at least. I look at it more like an interface specification, especially as there are several ways to write DDL - though there should really be a house style. For instance the NOT NULL constraint might be being added later on the script, so it isn't necessarily readable in the same way as normal code.
Yeah, in a perfect world everything in a database would be obvious from its name, but this is not a perfect world and naming things properly is extremely hard.
You're adding the information in "git diff" for the .sql-files for the commit to the comment?
Unfortunately, it does not include any information about what the last_name field does.