update images

README.md

 # Exploring the project
 
 - When the project opens, you should see a popup window appear named **Discover Fontainebleau**
-<img src = "https://github.com/Unity-Technologies/FontainebleauDemo/blob/master/Documentation/Images/DiscoverLevels.PNG" >
+<img src = "https://github.com/Unity-Technologies/FontainebleauDemo/blob/master/Documentation/Images/DiscoverLevels.png" >
-<img src = "https://github.com/Unity-Technologies/FontainebleauDemo/blob/master/Documentation/Images/DiscoverItems.PNG" >
+<img src = "https://github.com/Unity-Technologies/FontainebleauDemo/blob/master/Documentation/Images/DiscoverItems.png" >
   - The Discover tab allows you to inspect different interesting elements in the project and read small explanations.
 - Once the editor is ready, take a look at the menu bar : several menus are added compared to an empty Unity project. The **"Load levels" menu** offers you 2 options :
   - The **Day, Sunset, and Night buttons** are shortcut that will load the main scene plus one of the different lighting scenes used in the project but not the gameplay elements