parser: Add example dbus rule for unconfined peers

It may not be obvious that the peer label can be "unconfined". Provide
an example rule, in the apparmor.d man page, demonstrating the
peer=(label=unconfined) conditional.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>

parser/apparmor.d.pod

@@ -741,6 +741,9 @@ Example AppArmor DBus rules:
          member=ExampleMethod
          peer=(name=(com.example.ExampleName1|com.example.ExampleName2)),
 
+    # Allow receive access for all unconfined peers
+    dbus receive peer=(label=unconfined)),
+
     # Allow eavesdropping on the system bus
     dbus eavesdrop bus=system,