[MIG] base_import_match: Migration to 12.0

[UPD] README.rst

[UPD] Update base_import_match.pot

base_import_match/readme/DESCRIPTION.rst

@@ -0,0 +1,46 @@
+By default, when importing data (like CSV import) with the ``base_import``
+module, Odoo follows this rule:
+
+- If you import the XMLID of a record, make an **update**.
+- If you do not, **create** a new record.
+
+This module allows you to set additional rules to match if a given import is an
+update or a new record.
+
+This is useful when you need to sync heterogeneous databases, and the field you
+use to match records in those databases with Odoo's is not the XMLID but the
+name, VAT, email, etc.
+
+After installing this module, the import logic will be changed to:
+
+- If you import the XMLID of a record, make an **update**.
+- If you do not:
+
+  - If there are import match rules for the model you are importing:
+
+    - Discard the rules that require fields you are not importing.
+    - Traverse the remaining rules one by one in order to find a match in the database.
+
+      - Skip the rule if it requires a special condition that is not
+        satisfied.
+      - If one match is found:
+
+        - Stop traversing the rest of valid rules.
+        - **Update** that record.
+      - If zero or multiple matches are found:
+
+        - Continue with the next rule.
+      - If all rules are exhausted and no single match is found:
+
+        - **Create** a new record.
+  - If there are no match rules for your model:
+
+    - **Create** a new record.
+
+By default 2 rules are installed for production instances:
+
+- One rule that will allow you to update companies based on their VAT, when
+  ``is_company`` is ``True``.
+- One rule that will allow you to update users based on their login.
+
+In demo instances there are more examples.