[IMP] orm: add warning about model extension

When a model is defined with `_inherit` using a list, Odoo will do a check with the class name to set the `_name` of the model being extended. This is different than the previous versions and can be misleading

Author: emi-odoo

content/developer/reference/backend/orm.rst

@@ -1249,6 +1249,11 @@ will yield::
 
     {'name': "A", 'description': "Extended"}
 
+.. warning:: When :attr:`~odoo.models.Model._inherit` is set using a string,
+    this will also set the value of :attr:`~odoo.models.Model._name`.
+    In all the other cases the :attr:`~odoo.models.Model._name` is set by
+    the attribute itself or by the class name (i.e: ``class MyModel(models.Model)`` will be
+    translated into ``_name = 'my.model'``, even if not explicitly set)
 
 .. note::