added notes.

slides/why_use_git.md

 # Why use git?
 
-* keep the changes you made over time
-* allow you to backtrack (if necessary) and undo those changes
-* easily add contributions of your collaborators to the main code base
+* No need to fully rewrite code; reuse code and save time.
+* Keep the changes you made over time
+* Allow you to backtrack (if necessary) and undo those changes
+* Easily add contributions of your collaborators to the main code base
 
+note:
+
+Other points to mention: 
+* git shall not be considered as a nuisance, but as a tool that should help to track and trace the code.
+* git is not to track performance. Not using it shows exactly the opposite.