Update README.md

Author: jackbrookes

README.md

@@ -44,7 +44,7 @@ The settings is cascading, allowing setting independent variables at a `Session`
 
 A UI is available (but optional) allowing loading of participant data from file (or add new participant data). Variables that are collected are customisable and can be used in the experiment (e.g. a parameter for a participant's age could be used to change the difficulty of the experiment).
 
-![User interface](docs/media/screenshot-1.PNG)
+![User interface](docs/media/screenshot-1.png)
 
 ### File IO
 
@@ -130,4 +130,4 @@ This project is developed under Unity 2017.3.0f3.
 
 ## FAQ
 
-(In development)
+(In development)