Document all help keys in "git add -i" patch mode.

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

Documentation/git-add.txt

@@ -217,6 +217,8 @@ patch::
        k - do not decide on this hunk now, and view the previous
            undecided hunk
        K - do not decide on this hunk now, and view the previous hunk
+       s - split the current hunk into smaller hunks
+       ? - print help
 +
 After deciding the fate for all hunks, if there is any hunk
 that was chosen, the index is updated with the selected hunks.

git-add--interactive.perl

@@ -562,6 +562,7 @@ J - leave this hunk undecided, see next hunk
 k - leave this hunk undecided, see previous undecided hunk
 K - leave this hunk undecided, see previous hunk
 s - split the current hunk into smaller hunks
+? - print help
 EOF
 }