[DOC] Replace notebook with lab

I think it can be interesting as it simplifies the workflow:

For example you can see in different tabs the TP and the theory

README.md

@@ -41,7 +41,7 @@ conda activate formation_cpp_2020
 * Then you can run the notebook by going **into its root directory** (or internal links won't work...) in a terminal and typing:
 
 ```
-jupyter notebook
+jupyter lab
 ```
 
 __BEWARE__: I **strongly advise** to use a dedicated environment for the notebook: the ultimate goal is to use a real C++ environment for your project, and the anaconda environment hides the native C++ compiler on your machine.