Make example README URL into a link

Author: Artur Ostręga

example/README.md

@@ -12,6 +12,6 @@ Start a web server for the game.
 
 `$ bundle exec yeah server`
 
-Finally, visit http://localhost:1234 to run the game in your web browser.
+Finally, visit [http://localhost:1234](http://localhost:1234) to run the game in your web browser.
 
 Note: graphical output is in the works.