[docs] course format update note

Add an upgrade note about all YUI and 3.11 course format deprecation in
Moodle 5.0

Author: ferranrecio

docs/devupdate.md

@@ -55,3 +55,11 @@ Both of these values may be combined for plugins supporting both Moodle 4.5 and
 ```
 
 :::
+
+## Course formats
+
+<Since version="5.0" issueNumber="MDL-83527" />
+
+All course formats created for Moodle versions prior to 4.0, which still depend on the 3.11 libraries, will be deprecated starting from Moodle 5.0 and will no longer function in Moodle 6.0. We are discontinuing the use of YUI for course editing and transitioning the course display logic to output classes.
+
+To ensure a smooth transition, we have documented the migration process in detail. Please refer to the [migration guide](./apis/plugintypes/format/migration.md) for comprehensive instructions on updating your course formats to be compatible with the latest Moodle standards.