Also unify the formulation about --no-recurse-submodules for checkout
and switch, which we reuse for restore.

And correct the formulation about submodules' HEAD in read-tree, which
we reuse in reset.
Signed-off-by: NDamien Robert <damien.olivier.robert+git@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>