[ADD] required knowledge

Co-authored-by: Miquel Raïch <miquel.raich@forgeflow.com>
Co-authored-by: Pedro M. Baeza <pedro.baeza@tecnativa.com>

docsource/020_required_knowledge.rst

@@ -1,4 +1,32 @@
 Required Knowledge
 ==================
 
-TODO : write here prerequisites.
+To Use Openupgrade
+------------------
+
+* you should be able to launch an instance of Odoo on your local PC,
+  or on your server, **for each version of your migration**.
+* You should know how to get `openupgradelib`, obtained from the source repository, installed in your Python environment that is going to run the instance.
+* You should know how to invoke the odoo executable, injecting arguments for loading server wide modules and migrations path.
+  For example, if you're migrating from version 12.0 to 16.0,
+  you should be able to launch Odoo versions 13.0, 14.0, 15.0 and 16.0.
+
+* If you're migrating to a recent version,
+  you'll certainly have to reference numerous open pull requests on OCA/OpenUpgrade,
+  for the modules installed on your instance.
+  In this case, using the `gitaggregate <https://pypi.org/project/git-aggregator>`_
+  tool greatly facilitates the management of these numerous pull requests.
+
+To develop Openupgrade Scripts
+------------------------------
+
+- If you want to develop migration scripts for a given module, you need to have
+  complete functional (and technical) knowledge of this module.
+  For example, to develop migration scripts for `account` module from version 12.0
+  to 13.0, you need to master how account is working in version 12.0 and how
+  account is working in version 13.0.
+
+- Knowledge of SQL is a must if you need to write fast queries on huge amounts of data.
+
+- you need to have a good understanding of the functions provided
+  by the `openupgradelib <https://oca.github.io/openupgradelib/>`_ library.