Support Py_UNUSED() on clang (GH-13544)

diff --git a/Doc/c-api/intro.rst b/Doc/c-api/intro.rst
index b003bba..672936a 100644
--- a/Doc/c-api/intro.rst
+++ b/Doc/c-api/intro.rst
@@ -156,7 +156,7 @@
 .. c:macro:: Py_UNUSED(arg)
 
    Use this for unused arguments in a function definition to silence compiler
-   warnings, e.g. ``PyObject* func(PyObject *Py_UNUSED(ignored))``.
+   warnings. Example: ``int func(int a, int Py_UNUSED(b)) { return a; }``.
 
    .. versionadded:: 3.4