Add changelog entry

CHANGELOG.md

@@ -7,6 +7,13 @@ SPDX-License-Identifier: LicenseRef-GPL-2.0-only-with-DUNE-exception
 
 ## Build system: Changelog
 
+
+- Change the way include directories are set in dune projects. OLD behavior: use `include_directories`
+  in `dune_project` to globally set include dirs for all targets. NEW behavior: Provide a utility
+  `dune_default_include_directories` to set include dirs on targets manually. Which behavior to
+  activate can be decided in each module by using the new dune policy `DP0001`, which can be set
+  to `OLD` or `NEW` correspondingly.
+
 - The CMake function `dune_target_enable_all_packages` can now handle Interface libraries too.
 
 ## C++: Changelog