Upgrade: drop py 3.8/3.9. p.a.multilingual is core add-on.

Author: mauritsvanrees

docs/backend/upgrading/version-specific-migration/upgrade-to-61.md

@@ -68,4 +68,20 @@ This is a placeholder.
 ```{seealso}
 https://github.com/plone/plone.app.z3cform/pull/181
 ```
-````
+````
+
+## Drop Python 3.8 and 3.9
+
+We only support Python 3.10, 3.11, and 3.12.
+
+
+## `plone.app.multilingual` is a core add-on
+
+`plone.app.multilingual` is the package that adds multilingual support to Plone, so for having content in multiple languages.
+Until Plone 6.0 this was a dependency of `Products.CMFPlone`, so it was available for installation in all Plone sites.
+In Plone 6.1 it has become a dependency of the `Plone` package.
+
+If your project or your add-on needs this package, and you only depend on `Products.CMFPlone` until now, you should add `plone.app.multilingual` as dependency.
+Then your project or add-on will keep working in both Plone 6.0 and 6.1.
+
+The goal of turning more of the current core packages into core add-ons, is to make the core smaller, and in some cases solve circular dependencies.