Documentation/git-status: document porcelain status T (typechange)

Documentation/git-status: document porcelain status T (typechange)

As reported in [1], T is missing from the description of porcelain
status letters in git-status(1) (whereas T *is* documented in
git-diff-files(1) and friends). Document T right after M (modified)
because the two are very similar.

[1] https://github.com/fish-shell/fish-shell/issues/8311

Signed-off-by: Johannes Altmanninger <aclopte@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>