Add documentation for piwik_analytics

README.md

@@ -149,6 +149,13 @@ This will embed the google analytics tracking code.
 	{
 		"google_analytics": "UA-XXXXXXXXX-XX"
 	}
+	
+###Piwik Analytics:
+This will embed the piwik tracking code.
+
+	{
+		"piwik_analytics": "my-url-for-piwik.com"
+	}
 
 ## Running Locally