Add Backend None Documentation

doc/sphinx/reference/vcl.rst

@@ -286,6 +286,12 @@ parameters. The following attributes are available:
     Varnish reaches the maximum Varnish it will start failing
     connections.
 
+Empty backends can also be defined using the following syntax.::
+
+  backend name none;
+
+An empty backend will always return status code 503 as if it is sick.
+
 Backends can be used with *directors*. Please see the
 :ref:`vmod_directors(3)` man page for more information.
 

doc/sphinx/users-guide/vcl-backends.rst

@@ -31,6 +31,9 @@ Varnish can have several backends defined you can even join
 several backends together into clusters of backends for load balancing
 purposes.
 
+backends can also be empty or 'none' with the following syntax.::
+
+    backend default none;
 
 Multiple backends
 -----------------