update of the installation description

docs/source/installation.rst

@@ -22,17 +22,21 @@ Orfeo Toolbox (OTB) and its python bindings
     
 .. code-block:: console
 
-    sudo apt install otb-bin
-    # required by the python bindings
-    sudo apt install python3-numpy
-
-
+    wget https://www.orfeo-toolbox.org/packages/OTB-6.6.1-Linux64.run
+    chmod +x OTB-6.6.1-Linux64.run
+    ./OTB-6.6.1-Linux64.run
+    
     
-As indicated in the `OTB installation <https://www.orfeo-toolbox.org/CookBook/Installation.html#linux-x86-64>`_, do not forget to initialize the environment when you launch a new terminal:
+As indicated in the `OTB installation 
+<https://www.orfeo-toolbox.org/CookBook/Installation.html#linux-x86-64>`_, you need to modify some files to have functional OTB installation. To use Python3 you need in the file otbenv.profile modify ``lib/python`` into ``lib/python3``, for variable PYTHONPATH
 
+Then you can install Python Numpy for OTB bindings
+    
 .. code-block:: console
 
-    source otbenv.profile
+    # required by the python bindings
+    sudo apt install python3-numpy
+
 
 
 Sen2Cor