Update dashboard docs a bit.
Update dashboard docs a bit.

The documentation we had for the dashboard was missing a couple things
that have been added recently. This change adds them:

1. The "Overview" view (which we really aught to make the default)
   wasn't listed at all.
2. The new greyed-out mode for the "Ship It" indicators.

Testing Done:
Built HTML and checked output.

Reviewed at https://reviews.reviewboard.org/r/12654/

reviewboard/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard