Authors file update

AUTHORS.md

@@ -2,13 +2,9 @@
 
 This file lists all the individuals who have contributed to the development of the MOBILES project.
 
-## Principal Investigator
+## Principal Investigators
 - **Marie Lefevre** - Development Project Leader
-
-## Main Developer
 - **Raphaël Benedetto** - Principal Developer for the mobile application in Unity
-
-## Contributor
 - **Madjid Sadallah** - Contributor to the application and responsible for the implementation of the tracking and recommendation module
 
 ## Institutional Support