Make git status usage say git status instead of git commit

Make git status usage say git status instead of git commit

git status shares the same usage information as git commit since it
shows what would be committed if the same options are given.  However,
when displaying the usage information for git status it should say it
is for git status not git commit.

Signed-off-by: Shawn Bohrer <redacted>
Signed-off-by: Junio C Hamano <redacted>