completion: add option '--recurse-submodules' to 'git clone'

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -1091,6 +1091,7 @@ _git_clone ()
 			--depth
 			--single-branch
 			--branch
+			--recurse-submodules
 			"
 		return
 		;;