bash completion: Add 'workflows' to 'git help'

Completion for new workflow documentation introduced in f948dd8

Signed-off-by: Lee Marlow <lee.marlow@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/completion/git-completion.bash

@@ -881,6 +881,7 @@ _git_help ()
 		attributes cli core-tutorial cvs-migration
 		diffcore gitk glossary hooks ignore modules
 		repository-layout tutorial tutorial-2
+		workflows
 		"
 }