completion: add more parameter value completion

This adds value completion for a couple more paramters. To make it
easier to maintain these hard coded lists, add a comment at the original
list/code to remind people to update git-completion.bash too.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pretty.c

@@ -98,6 +98,10 @@ static void setup_commit_formats(void)
 		{ "fuller",	CMIT_FMT_FULLER,	0,	8 },
 		{ "full",	CMIT_FMT_FULL,		0,	8 },
 		{ "oneline",	CMIT_FMT_ONELINE,	1,	0 }
+		/*
+		 * Please update $__git_log_pretty_formats in
+		 * git-completion.bash when you add new formats.
+		 */
 	};
 	commit_formats_len = ARRAY_SIZE(builtin_formats);
 	builtin_formats_len = commit_formats_len;