docs(@angular/cli): add bypass proxy example

Author: justinkurtz

docs/documentation/stories/proxy.md

@@ -56,3 +56,31 @@ and make sure to point to the right file
 ```json
 "start": "ng serve --proxy-config proxy.conf.js",
 ```
+
+### Bypass the Proxy
+
+If you need to optionally bypass the proxy, or dynamically change the request before it's sent,  define the configuration in proxy.conf.js e.g.
+
+```js
+const PROXY_CONFIG = {
+    "/api/proxy": {
+        "target": "http://localhost:3000",
+        "secure": false,
+        "bypass": function (req, res, proxyOptions) {
+            if (req.headers.accept.indexOf("html") !== -1) {
+                console.log("Skipping proxy for browser request.");
+                return "/index.html";
+            }
+            req.headers["X-Custom-Header"] = "yes";
+        }
+    }
+}
+
+module.exports = PROXY_CONFIG;
+```
+
+again, make sure to point to the right file
+
+```json
+"start": "ng serve --proxy-config proxy.conf.js",
+```