Add data load instructions to dev install doc

If you follow the steps as curently described, you end up with a pretty
useless setup (with no projects created, there is only so much you can
do). This commit adds an optional section about load_projects and
load_superusers to the install instructions.

Change-Id: I97856c96af4adc3a0c89de0b7738e03f3bce4a5f
Merge "Add data load instructions to dev install doc"