Added info on --skip-tags to tags documentation.

docsite/rst/playbooks_tags.rst

@@ -24,6 +24,10 @@ Example::
 If you wanted to just run the "configuration" and "packages" part of a very long playbook, you could do this::
 
     ansible-playbook example.yml --tags "configuration,packages"
+    
+On the other hand, if you want to run a playbook *without* certain tasks, you could do this::
+
+    ansible-playbook example.yml --skip-tags "notification"
 
 You may also apply tags to roles::