update readme with usage example and options

Author: respectTheCode

README.md

@@ -2,6 +2,24 @@
 
 Datadog middleware for Connect JS / Express
 
+
+## Usage
+
+Add middleware immediately before your router.
+
+	app.use(require("connect-datadog")({}));
+	app.use(app.router);
+
+## Options
+
+All options are optional.
+
+* `dogstatsd` node-dogstatsd client. `default = new require("node-dogstatsd").StatsD()`
+* `stat` *string* name for the stat. `default = "node.express.router"`
+* `tags` *array* of tags to be added to the histogram. `default = []`
+
+
 ## License
 
 View the [LICENSE](https://github.com/AppPress/node-connect-datadog/blob/master/LICENSE) file.
+