Add upgrade guide to the documentation
[skip ci]
diff --git a/docs/changelog.rst b/docs/changelog.rst
index f4b99c5..80c156f 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -60,7 +60,8 @@
* pybind11's headers and build system now more strictly enforce hidden symbol
visibility for extension modules. This should be seamless for most users,
- but see the upgrade guide if you use a custom build system.
+ but see the :doc:`upgrade` if you use a custom build system.
+ `#995 <https://github.com/pybind/pybind11/pull/995>`_.
* Support for ``py::module_local`` types which allow multiple modules to
export the same C++ types without conflicts. This is useful for opaque