alembic Add docs for data migrations

I added a small docs regarding data migrations, based on #972.

This pull request is:

[X] A documentation / typographical error fix
- Good to go, no issue or tests are needed

Have a nice day!

May 26 '22 08:05 ziima

these are good, I would want to edit them stylistically so let me pull them into gerrit and I'll try to look in the coming days.

Jun 04 '22 14:06 zzzeek

New Gerrit review created for change c985e0d8096e750df35aa07dde71f432a57656b6: https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/3895

Jun 04 '22 14:06 sqla-tester

mike bayer (zzzeek) wrote:

recheck

View this in Gerrit at https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/3895

Sep 09 '22 14:09 sqla-tester

mike bayer (zzzeek) wrote:

recheck

i tried to fix jenkins but did it wrong, attempt # 2

View this in Gerrit at https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/3895

Sep 09 '22 15:09 sqla-tester

Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/3895 has been merged. Congratulations! :)

Apr 02 '23 17:04 sqla-tester