[DOC] Describe how to propose a migration script to the community. (g…

…it command, commit name convention, etc.)

Co-authored-by: Pedro M. Baeza <pedro.baeza@tecnativa.com>

docsource/090_contribute.rst

@@ -10,6 +10,47 @@ In order to contribute to the OpenUpgrade project, please
   database, and give back any code improvements developed during the project.
 
 
+How to contribute new migration scripts
+---------------------------------------
+
+To Contribute to OpenUpgrade you must make one pull request per module.
+
+For example, if you want to propose the migration script of the ``account``
+module from version 15.0 to version 16.0:
+
+  * Always ensure that there is no work already in progress by a community member.
+    For that purpose, go the issue named "Migration to version NN.0" on GitHub, where NN is the version for which you want to propose the script.
+    `here <https://github.com/OCA/OpenUpgrade/issues/3681/>`_.
+
+    Sometimes, the pull request is not yet registered in the issue, so it's not bad to do a search on the opened pull requests with the name of the module to look for.
+
+  * Then, ensure that all the dependencies of the module are mark as ``done`` or
+    ``Nothing to do`` in OpenUpgrade for that version.
+    For that purpose, refer to :doc:`030_coverage_analysis`.
+    In our example, check the ``depends`` key of the `manifest <https://github.com/odoo/odoo/blob/16.0/addons/account/__manifest__.py#L18>`_ of the ``account`` module 
+    If some dependencies are missing, you should start by migrating these modules.
+
+  * As other OCA contribution, create a new branch, from an up to date OCA branch:
+
+    ``git checkout -b 16.0-mig-account``
+
+  * Make a copy of the analysis file with the suffix ``_work``.
+
+    ``cd ./openupgrade_scripts/scripts/account/16.0.1.2/``
+    ``cp upgrade_analysis.txt upgrade_analysis_work.txt``
+
+  * Explain the changes to do in the ``upgrade_analysis_work.txt``.
+    Write ``pre-migration.py`` and / or ``post-migration.py`` scripts in the same folder.
+    Comment / uncomment lines in ``noupdate_changes.xml``.
+    (Read more in :doc:`080_migration_script_development`)
+
+  * Finally, commit your changes.
+    ``git add . && git commit -am "[OU-ADD] account"``
+    (For a fix, use ``[OU-FIX]`` prefix)
+
+  * Propose your changes to the community for review.
+    ``git push MY_REMOTE 16.0-mig-account``
+
 Community involvement
 ---------------------