Clarify that in the Webapp Developer Environment, the DB must be migrated before any management commands are run that manipulate the DB

On the page Webapp Developer Environment, it should be clarified (with a note?) in the Getting started with a project section that the DB must be migrated before any manage_development.sh commands are run to manipulate the DB (other than manage_development.sh migrate of course).

Relates to uis/devops/uga/smi#239