doc: fix the bnf like style of some commands

In command line options, variables are entered between < and >

Signed-off-by: Jean-Noël Avila <jn.avila@free.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-init.txt

@@ -70,7 +70,7 @@ repository.
 +
 If this is reinitialization, the repository will be moved to the specified path.
 
--b <branch-name::
+-b <branch-name>::
 --initial-branch=<branch-name>::
 
 Use the specified name for the initial branch in the newly created repository.

builtin/submodule--helper.c

@@ -1308,7 +1308,7 @@ static int module_summary(int argc, const char **argv, const char *prefix)
 	};
 
 	const char *const git_submodule_helper_usage[] = {
-		N_("git submodule--helper summary [<options>] [commit] [--] [<path>]"),
+		N_("git submodule--helper summary [<options>] [<commit>] [--] [<path>]"),
 		NULL
 	};