Issue #11768: signal.set_wakeup_fd() and PySignal_SetWakeupFd() added in 2.6

Fix the documentation.
diff --git a/Doc/c-api/exceptions.rst b/Doc/c-api/exceptions.rst
index e9ced0b..8b1e8fc 100644
--- a/Doc/c-api/exceptions.rst
+++ b/Doc/c-api/exceptions.rst
@@ -347,6 +347,8 @@
    error checking.  *fd* should be a valid file descriptor.  The function should
    only be called from the main thread.
 
+   .. versionadded:: 2.6
+
 
 .. cfunction:: PyObject* PyErr_NewException(char *name, PyObject *base, PyObject *dict)