The only documentation about googles \'repo\' tool for android repository management was:
https://sites.google.com/a/android.com/opensource/download/using-repo
Documentation about repo
is a bit hard to come about, as you have discovered.
In addition to your link, the repo help
commands are very useful. E.g. repo help manifest
and repo help sync
are quite well described.
Also if you look in your .repo/repo/docs/manifest-format.txt
there are very decent description of the manifest system used by the Android repo program.
If you discover additional resources of information on repo
I would be very interested in hearing about it. :)