"log --pretty" documentation: do not forget "tformat:"
"log --pretty" documentation: do not forget "tformat:"

We forgot to list "tformat:<string>" when enumerating possible
values that "--pretty=<format>" can take.  It was not described
that "--pretty='string with %s placeholder'" that is not understood
is DWIMmed as "--pretty=tformat:<that string>".

Further, it was unclear what "When omitted, defaults to 'medium'"
was meant.  Is it "When --pretty=<something> was not given at all",
or is it "When --pretty is given without =<something>"?  Clarify
that it is the latter.

Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git