add upgrading notes

Author: michalsn

user_guide_src/source/installation/upgrade_470.rst

@@ -44,12 +44,13 @@ and it is recommended that you merge the updated versions with your application:
 Config
 ------
 
-- @TODO
+- app/Config/Migrations.php
+    - ``Config\Migrations::$lock`` has been added, with a default value set to ``false``.
 
 All Changes
 ===========
 
 This is a list of all files in the **project space** that received changes;
 many will be simple comments or formatting that have no effect on the runtime:
 
-- @TODO
+- app/Config/Migrations.php