MAINTAINERS: add and correct types of some "T:" entries

Tree location entries should start with the appropriate type.

Add git to some, hg to another.

Neaten tree type description.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>