ls-remote: document the '--get-url' option

While looking for a way to expand the URL of a remote
that uses a 'url.<name>.insteadOf' config option I stumbled
over the undocumented '--get-url' option of 'git ls-remote'.
This adds some minimum documentation for that option.

And while at it, also add that option to the '-h' output.

Signed-off-by: Stefan Naewe <stefan.naewe@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-ls-remote.txt

@@ -42,6 +42,11 @@ OPTIONS
 	it successfully talked with the remote repository, whether it
 	found any matching refs.
 
+--get-url::
+	Expand the URL of the given remote repository taking into account any
+	"url.<base>.insteadOf" config setting (See linkgit:git-config[1]) and
+	exit without talking to the remote.
+
 <repository>::
 	Location of the repository.  The shorthand defined in
 	$GIT_DIR/branches/ can be used. Use "." (dot) to list references in

builtin/ls-remote.c

@@ -5,7 +5,7 @@
 
 static const char ls_remote_usage[] =
 "git ls-remote [--heads] [--tags]  [-u <exec> | --upload-pack <exec>]\n"
-"                     [-q|--quiet] [--exit-code] [<repository> [<refs>...]]";
+"                     [-q|--quiet] [--exit-code] [--get-url] [<repository> [<refs>...]]";
 
 /*
  * Is there one among the list of patterns that match the tail part