added changelog entry

Author: wjakob

docs/changelog.rst

@@ -15,6 +15,7 @@ See :ref:`upgrade-guide-2.6` for help upgrading to the new version.
   switches the binding target to size-based optimization regardless global
   CMake build type (except in debug mode, where optimizations remain disabled).
   This reduces binary size quite substantially (~25%).
+  `#2463 <https://github.com/pybind/pybind11/pull/2463>`_
 
 * Keyword-only argument supported in Python 2 or 3 with ``py::kw_only()``.
   `#2100 <https://github.com/pybind/pybind11/pull/2100>`_