CHANGELOG: add --boxed deprecation to 2.5.0

Author: bluetech

CHANGELOG.rst

@@ -1,6 +1,12 @@
 pytest-xdist 2.5.0 (2021-12-10)
 ===============================
 
+Deprecations and Removals
+-------------------------
+
+- `#468 <https://github.com/pytest-dev/pytest-xdist/issues/468>`_: The ``--boxed`` commmand line argument is deprecated. Install pytest-forked and use ``--forked`` instead. pytest-xdist 3.0.0 will remove the ``--boxed`` argument and pytest-forked dependency.
+
+
 Features
 --------