Update UserManual.md

Short form subnets (like 192.168/16) are malformed from before.
The description of the default behavior was wrong.

docs/UserManual.md

@@ -148,11 +148,12 @@ subnet is pre-pended by either a `-` or a `+` sign. A plus sign means allow,
 where a minus sign means deny. If a subnet mask is omitted, such as `-1.2.3.4`,
 this means to deny only that single IP address.
 
-Subnet masks may vary from 0 to 32, inclusive. The default setting is to allow
-all accesses. On each request the full list is traversed, and
+If this value is not set, all accesses are allowed. Otherwise, the default
+setting is to deny all accesses. On each request the full list is traversed, and
 the last match wins. Examples:
 
-    -0.0.0.0/0,+192.168/16    deny all accesses, only allow 192.168/16 subnet
+    +192.168.0.0/16,+fe80::/64    deny all accesses, allow 192.168.0.0/16 and fe80::/64 subnet
+                                  (The second one is valid only if IPv6 support is enabled)
 
 To learn more about subnet masks, see the
 [Wikipedia page on Subnetwork](http://en.wikipedia.org/wiki/Subnetwork).
@@ -693,6 +694,7 @@ list of key=value pairs, where key could be:
 
     *                   limit speed for all connections
     x.x.x.x/mask        limit speed for specified subnet
+    [IPv6-addr]/mask    limit speed for specified IPv6 subnet (needs square brackets)
     uri_prefix_pattern  limit speed for given URIs
 
 The value is a floating-point number of bytes per second, optionally