show-ref: place angle brackets around variables in usage string

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/show-ref.c

@@ -8,7 +8,7 @@
 
 static const char * const show_ref_usage[] = {
 	N_("git show-ref [-q | --quiet] [--verify] [--head] [-d | --dereference] [-s | --hash[=<n>]] [--abbrev[=<n>]] [--tags] [--heads] [--] [<pattern>...]"),
-	N_("git show-ref --exclude-existing[=pattern] < ref-list"),
+	N_("git show-ref --exclude-existing[=<pattern>] < <ref-list>"),
 	NULL
 };