Mention that with windows target hosts, fact_path and filter are not currently supported

library/system/setup

@@ -54,6 +54,8 @@ notes:
       install I(facter) and I(ohai) means you can avoid Ruby-dependencies on your
       remote systems. (See also M(facter) and M(ohai).)
     - The filter option filters only the first level subkey below ansible_facts.
+    - If the target host is Windows, you will not currently have the ability to use
+      C(fact_path) or C(filter).
 author: Michael DeHaan
 '''