Improved installation instructions.

docs/source/installation.rst

@@ -5,26 +5,34 @@ Installation
 Installing sen2chain
 --------------------
 
-This package requires Python 3, GDAL and `Sen2Cor <http://step.esa.int/main/third-party-plugins-2/sen2cor/>`_.
+This package requires Python 3, GDAL, OTB and `Sen2Cor <http://step.esa.int/main/third-party-plugins-2/sen2cor/>`_.
 
 .. note:: The current version of sen2chain is not available on Windows.
 
-From Pypy
-^^^^^^^^^
+
+Prerequisites
+^^^^^^^^^^^^^
+GDAL and OTB
+
+.. code-block:: console
+
+    sudo apt install gdal-bin libgdal-dev python3-gdal otb-bin python3-otb
+    
+Sen2Cor
 
 .. code-block:: console
 
-    pip3 install sen2chain
+    wget http://step.esa.int/thirdparties/sen2cor/2.5.5/Sen2Cor-02.05.05-Linux64.run
+    chmod +x Sen2Cor-02.05.05-Linux64.run && ./Sen2Cor-02.05.05-Linux64.run
 
-From sources
-^^^^^^^^^^^^
+Install sen2chain from sources
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. code-block:: console
 
     git clone https://framagit.org/jebins/sen2chain.git
     cd sen2chain
-    pip3 install -r requirements.txt
-    pip3 install -e .
+    pip3 install --user -e .
 
 
 Configuration