Fix localhost link

lessons/03-navigating-with-link/README.md

@@ -25,7 +25,7 @@ export default React.createClass({
 })
 ```
 
-Now visit http://localhost:8080/ and click the links, click back, click
+Now visit [http://localhost:8080](http://localhost:8080) and click the links, click back, click
 forward. It works!
 
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