updated description in index.rst

Signed-off-by: Stefano Bernagozzi <[email protected]>

docs/source/index.rst

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 CONVINCE model2code Documentation
 ==================================
-Welcome to the model2code tool documentation. 
+This is the documentation for the CONVINCE model2code tool. The tool is developed as part of the CONVINCE project.
+The tool is used mainly to generate skill level code starting from an SCXML model.
+The inputs of the program are: 
+- an SCXML model that describes the behavior of the skill,
+- an XML file that describes the full model of the program, which includes the behavior tree, the skills and the components used in the system,
+- an XML file that describes the interfaces used between behavior tree and skills, and between skills and components.
+
+The output of the program is composed of:
+
+- a C++ file that contains the code of the skill,
+- an header file that contains the declaration of the skill.
+
+the output above is only if the datamodel is ecmascript, otherwise you will need to add the parameter ``--datamodel_mode`` in order to generate also the C++ datamodel files. 
+In this case you will get 2 other files:
+
+- a C++ file that contains the code of the datamodel,
+- an header file that contains the declaration of the datamodel. 
+
+In order to complete the code generation you need to write a CMakeLists.txt file that includes the generated files, a main file that includes the skill header and a package.xml in order to create a ROS package.
+
+
+The parameters required to run the program are:
+
+- ``--input_filename`` : the path to the SCXML file that describes the behavior of the skill,
+- ``--model_filename`` : the path to the XML file that describes the full model of the program,
+- ``--interface_filename`` : the path to the XML file that describes the interfaces used.
+
+by default the program will generate the code in the directory where the SCXML file passed by the parameter ``--input_filename`` is located, but you can specify a different directory by using the parameter ``--output_path``.
+
 
 Contents
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