Update README.md

README.md

@@ -5,6 +5,8 @@
 You need *xeyes* program.
 *xeyes* is part of the x11 suite of programs included in all linux distributions.
 
+You also need *PyGTK* installed. If not, `sudo apt-get install python-gtk2`.
+
 ## How to use it ?
 Clone this project and run :
 ```