Update README.md

Author: ctroupin

README.md

@@ -3,7 +3,7 @@ Examples of commands to create plots of DIVA input and ouput : data, contours, f
 
 # Contours
 
-![alt text](https://cloud.githubusercontent.com/assets/11868914/10428025/ac593fec-70ee-11e5-8142-41dbefecca1c.png)
+![Contour](https://cloud.githubusercontent.com/assets/11868914/10428025/ac593fec-70ee-11e5-8142-41dbefecca1c.png)
 
 # Finite-element mesh