standardize usage info string format

This patch puts the usage info strings that were not already in docopt-
like format into docopt-like format, which will be a litle easier for
end users and a lot easier for translators. Changes include:

- Placing angle brackets around fill-in-the-blank parameters
- Putting dashes in multiword parameter names
- Adding spaces to [-f|--foobar] to make [-f | --foobar]
- Replacing <foobar>* with [<foobar>...]

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Reviewed-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/checkout-index.c

@@ -123,7 +123,7 @@ static void checkout_all(const char *prefix, int prefix_length)
 }
 
 static const char * const builtin_checkout_index_usage[] = {
-	N_("git checkout-index [options] [--] [<file>...]"),
+	N_("git checkout-index [<options>] [--] [<file>...]"),
 	NULL
 };