[plt-dev] Revised git intro text

I've finished most of the git "intro" text.  It's no longer the quick
intro thing that I though it would be (it's 8.5 times bigger than the
previous version), but it should be easy to read through and has
everything that you'll need to know for a while.

*Please* read it.

It's not finished yet -- the (important) missing parts are the ones on
branches, using a private clone, and workflow suggestions, but it
should be enough for the kind of day-to-day work that almost everyone
is currently doing.  I'll send another note when I'm done with that.

Also, in case anyone has any suggestions, corrections, clarifications,
or other whateverations, please tell me.  Writing this thing (instead
of actually hacking code) is something that I would be *very* happy to
not do -- so help would be highly appreciated.

(And from now on, if I add bits to existing text I'll say something
about it, instead of asking people to re-read the whole thing...)

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!