Update README.md

small typo fix

Author: davidpodhola

README.md

@@ -31,7 +31,7 @@ For convenience, we have a live API server running at https://conduit.production
 
 The source code for the backend server (available for Node, Rails and Django) can be found in the [main RealWorld repo](https://github.com/gothinkster/realworld).
 
-If you want to change the API URL to a local server, simply edit `src/agent.js` and change `API_ROOT` to the local server's URL (i.e. `localhost:3000/api`)
+If you want to change the API URL to a local server, simply edit `src/agent.js` and change `API_ROOT` to the local server's URL (i.e. `http://localhost:3000/api`)
 
 
 ## Functionality overview