Make <tutorial url> explicit

Make the setup fast and easy :)

lessons/01-setting-up/README.md

@@ -9,7 +9,7 @@ up our project.
 ## Clone the Tutorial
 
 ```
-git clone <tutorial url>
+git clone https://github.com/reactjs/react-router-tutorial
 cd react-router-tutorial
 cd lessons/01-setting-up
 npm install