documented new config options

README.md

@@ -162,6 +162,10 @@ on how to deploy run headless Chrome in Docker.
 When deploying the service, set configuration variables by including a `config.json` in the
 root. Available configuration options:
  * `datastoreCache` default `false` - set to `true` to enable caching on Google Cloud using datastore
+ * `timeout` default `10000` - set the timeout used to render the target page. 
+ * `port` default `3000` - set the port to use for running and listening the rendertron service. Note if process.env.PORT is set, it will be used instead.
+ * `width` default `1000` - set the width (resolution) to be used for rendering the page.
+ * `height` default `1000` - set the height (resolution) to be used for rendering the page.
 
 ### Troubleshooting
 If you're having troubles with getting Headless Chrome to run in your