gitcli: document --end-of-options

Now that --end-of-options is available for any users of
setup_revisions() or parse_options(), which should be effectively
everywhere, we can guide people to use it for all their disambiguating
needs.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gitcli.txt

@@ -37,6 +37,12 @@ arguments.  Here are the rules:
    file called HEAD in your work tree, `git diff HEAD` is ambiguous, and
    you have to say either `git diff HEAD --` or `git diff -- HEAD` to
    disambiguate.
+
+ * Because `--` disambiguates revisions and paths in some commands, it
+   cannot be used for those commands to separate options and revisions.
+   You can use `--end-of-options` for this (it also works for commands
+   that do not distinguish between revisions in paths, in which case it
+   is simply an alias for `--`).
 +
 When writing a script that is expected to handle random user-input, it is
 a good practice to make it explicit which arguments are which by placing