CREATE_INDEX and CREATE_INDEX_EXCLUSIVE docs are not helpful

[sobolevn]

Hi! Thanks for working on this project.
Today I updated to v5 and got some new CI failures.

Here's my migration file: https://github.com/tough-dev-school/python-testing-homework/blob/master/server/apps/identity/migrations/0001_initial.py

It generate this warning:

(pictures, 0001_initial)... WARNING (cached)
        CREATE INDEX prolongs transaction, delaying lock release

It is not clear from the docs on how to fix this warning. This forced me to switch it off for now.

[David-Wobrock]

Hey @sobolevn

Fair point, thanks for raising it 👍
I'll tackle that :)