Please see https://alembic.readthedocs.org/en/latest/index.html for general documentation

To create alembic migrations you need to have alembic installed and available in PATH:
# pip install alembic
$ cd ./taskflow/persistence/backends/sqlalchemy/alembic
$ alembic revision -m "migration_description"

See Operation Reference https://alembic.readthedocs.org/en/latest/ops.html#ops
for a short list of commands
