Adding or creating a development is really easy to do; as an Administrator, click the "Admin" drop-down in the top-right, then click into "Developments" (Admin > Developments).
Once you are in the admin view of developments, there will be a blue link on the top-left side titles "+ Add new Development". Clicking this will take you to a form with a few fields to fill in, like the name of the development, the address it is located, and additional info that may need to be recorded in the development.