Make the main about page more useful

Add a description and keywords and bring the page up to date. This
also expands its content a little (while trying to keep it fairly
brief) while adding more links to the other /about/* pages.

Patch set 2: tweak age range to be less specific, note that it's
             (mostly) the game which changes each year, clarify that
             the kit is a robotics kit.
Patch set 3: grammar tweaks.
Patch set 3: another grammar tweak.

Change-Id: I462e53f498d038d5890cf474af7cbead1a091507
Add a page about kit assembly

This includes topology documentation for the boards and embeds
the youtube how-to video on the same topic.

Patch set 2: s/camcon/CamCon/.

Change-Id: If3d0d9b2d91fbf5816670df1255a0e01e707eb69