policy: document that you can pass lists to FORWARD

... and that the length is limited.

modules/policy/README.rst

@@ -24,7 +24,8 @@ There are several defined actions:
 * ``DENY`` - return NXDOMAIN answer
 * ``DROP`` - terminate query resolution, returns SERVFAIL to requestor
 * ``TC`` - set TC=1 if the request came through UDP, forcing client to retry with TCP
-* ``FORWARD(ip)`` - forward query to given IP and proxy back response (stub mode)
+* ``FORWARD(ip)`` - forward query to given IP and proxy back response (stub mode);
+  it can be a single IP (string) or a list of up to four IPs.
 * ``MIRROR(ip)`` - mirror query to given IP and continue solving it (useful for partial snooping)
 * ``REROUTE({{subnet,target}, ...})`` - reroute addresses in response matching given subnet to given target, e.g. ``{'192.0.2.0/24', '127.0.0.0'}`` will rewrite '192.0.2.55' to '127.0.0.55', see :ref:`renumber module <mod-renumber>` for more information.