Updating the access_mode setting description.

Access mode didn't list the possible values or an explanation to how that mapped to the Grafana Admin UI. Formatting to be like the other provider documentation. Closes #92

Author: phillipsj

website/docs/r/data_source.html.md

@@ -94,9 +94,10 @@ The following arguments are supported:
   database to use on the selected data source server.
 
 * `access_mode` - (Optional) The method by which the browser-based Grafana
-  application will access the data source. The default is "proxy", which means
+  application will access the data source. The default is `proxy`, which means
   that the application will make requests via a proxy endpoint on the Grafana
-  server.
+  server. Proxy is displayed in the Grafana admin as Server. Another possible value is 
+  `direct` which is displayed in the Grafana admin as Browser.
 
 JSON Data (`json_data`) supports the following: