A *working* alembic example in the docs

[dekoza]

The docs regarding alembic integration are too laconic to be considered useful for beginners. They look more like reminders for folks that have at least 5 years of alembic experience under their belt.

I wish the examples provided there would have all imports in place. E.g. where I should take metadata from? How does that my_models file looks like if I have the metadata exposed there?

If I have several apps with models in them - what then? What should I prepare to feed the alembic config?

There are some tutorials in the wild but they use old ormar (pre 0.20). They can be ported with a little work but I think such examples should be a part of the official docs.