Add sample for proxy usage

Author: petehouston

README.md

@@ -280,6 +280,24 @@ need to update the `helpers.WebDriverIO.proxy` key.
 }
 ```
 
+For example,
+
+```js
+{
+    "helpers": {
+        "WebDriverIO": {
+            "proxy": {
+                "proxyType": "manual",
+                "httpProxy": "http://corporate.proxy:8080",
+                "socksUsername": "codeceptjs",
+                "socksPassword": "secret",
+                "noProxy": "127.0.0.1,localhost"
+            }
+        }
+    }
+}
+```
+
 Please refer to [Selenium - Proxy Object](https://code.google.com/p/selenium/wiki/DesiredCapabilities#Proxy_JSON_Object) for more information.
 
 ## Current State