Updated readme.

Signed-off-by: Alistair Kearney <alistair@21degrees.com.au>

README

@@ -29,3 +29,13 @@ stored in the Symphony config file, and page type is matched against these mappi
 	   be set. Should more than one match be found, the last one encountered will be
 	   used.
 
+
+[CONTENT DISPOSITION]
+	To force download of a page (by setting the Content-Disposition header), give it a page 
+	type that begins with a '.'. The page will be downloaded with a filename = $page-handle.$type.
+	For instance, a page with handle 'form-data' and a page type of '.csv' will be downloaded as
+	'form-data.csv'.
+
+	Depending on the Content Type you map to a page type, it may not be necessary to add this
+	Content-Disposition header in order to cause the page to download.
+