Update changelog for v2.2.0

[skip ci]
diff --git a/docs/advanced/functions.rst b/docs/advanced/functions.rst
index a7807dc..0e2b16c 100644
--- a/docs/advanced/functions.rst
+++ b/docs/advanced/functions.rst
@@ -406,6 +406,8 @@
     need to specify a ``py::arg()`` annotation for each argument with the
     no-convert argument modified to ``py::arg().noconvert()``.
 
+.. _none_arguments:
+
 Allow/Prohibiting None arguments
 ================================