Update README alembic migration command
Update README alembic migration command

Updated README application deployment notes to show using ./env/bin/alembic.  I got an error when using the latest version of alembic installed from pip. I'm guessing it is always best to use the same version installed by the project?
ethan-nelson/osm-tasking-manager2,ethan-nelson/osm-tasking-manager2,ethan-nelson/osm-tasking-manager2,ethan-nelson/osm-tasking-manager2