Number contribution steps to add a new description

Author: stephane-caron

CONTRIBUTING.md

@@ -11,11 +11,14 @@ This project's goal is to facilitate loading and sharing of robot descriptions f
 
 Make sure that your pull request satisfies the following:
 
-- The robot description is distributed legally and under an open source license (permissive or copyleft)
-- The file name for the new submodule is ``<robot_name>_description.py`` in snake-case. For example, ``R2D2_description`` becomes ``r2d2_description.py``
-- If needed, add the repository containing the new description to ``_repositories.py``.
+1. **License:** The robot description is distributed legally and under an open source license (permissive or copyleft).
+2. **Repository:** If needed, add the repository containing the new description to ``_repositories.py``.
     - Use a specific git commit ID. This way the robot description will still work in the interval between a change in the file structure of the target repository and the corresponding update in `robot_descriptions`.
-- Add the description metadata to the ``DESCRIPTIONS`` dictionary in ``_descriptions.py``
-- Check that all unit tests are successful by ``tox -e py3X`` where ``3.X`` is the version of your Python interpreter
-- Document the description's submodule name in the Descriptions section of the [README](README.md)
-- Write down the new model to the [changelog](CHANGELOG.md)
+3. **Submodule:** add a Python file for the robot descriptions to ``robot_descriptions/``.
+    - The file name for the new submodule is ``<robot_name>_description.py`` in snake-case.
+    - For example, the file name for the Kinova (maker) Gen2 (robot name) is ``gen2_description.py``.
+    - Use the ``mj_description`` suffix for an MJCF description.
+4. **Listing:** Add the description metadata to the ``DESCRIPTIONS`` dictionary in ``_descriptions.py``.
+5. **Testing:** Check that all unit tests are successful by ``tox -e py``.
+6. **README:** Document the description's submodule name in the Descriptions section of the [README](README.md).
+7. **Changelog:** Write down the new model to the [changelog](CHANGELOG.md).