Follow-up from "Restructure/improve docs"

The following discussion from !1314 (merged) should be addressed:

• @jovuit started a discussion: (+2 comments)

  Also regarding the server migration doc, I did only change for the non docker setup. I am not sure whether the docker setup also needs to be changed accordingly, as the commands where somewhat different.

  I have no docker setup to test this, and I am not familiar with docker. Can someone please confirm if the pg_restore command for docker is correct as is, or if it must be updated to use psql as well?

  Old:

  docker exec -i funkwhale_postgres_1 pg_restore -c -U postgres -d postgres < "db.dump"

  Suggested new:

  docker exec -i funkwhale_postgres_1 psql -U postgres -d postgres db.dump

  I can commit accordingly if someone confirms.