Add better instructions for flask migrate

README.md

@@ -68,14 +68,29 @@ curl http://localhost:5000/connectors
 
 ## Database changes
 
-If there any changes made to the model run the migrate command (example commment)
+If there any changes made to the model first ensure that it is added to the list of imports in
+`backend/app/__init_.py` before the following line
+
+```
+migrate = Migrate(app, db)
+```
+
+This allows alembic and flask migrate to see all the models in use so the migrations can be
+generated correctly.
+
+Once that is done, then you need to run the migrate command (example commment)
 and if any changes were detected, update your local DB instance.
 
 ```
 FLASK_APP=copilot.py flask db migrate -m "Add User model."
 FLASK_APP=copilot.py flask db upgrade
 ```
 
+Review the generated migration file to make sure the changes to the databse make sense in terms
+of what is needed to upgrade from the previous state, and then to downgrade to remove this migration.
+
+Don't forget to commit the new migration file into git.
+
 See https://flask-migrate.readthedocs.io/en/latest/ for further information
 
 # Deployment