Update templates.asciidoc

I've been attempting to programatically verify that adding index templates via the `{path.conf}/templates/` directory works fine although I was never able to validate this via an API call to the `/_template/`.  It seems that these templates do not appear in that API call, which I discovered in the following mail thread:

http://elasticsearch-users.115913.n3.nabble.com/Loading-of-index-settings-template-from-file-in-config-templates-td4024923.html#d1366317284000-912

My question is why wouldn't the `/_template/*` method return these templates?  This tends to complicate things for those that want to perform automated tests to verify that they are in fact being recognized and used by Elasticsearch.

docs/reference/indices/templates.asciidoc

@@ -191,3 +191,5 @@ added if it matches an index. Here is a sample of the mentioned file:
     }
 }
 --------------------------------------------------
+
+*Please note that templates added this way will not appear in the `/_template/*` API request.*