Add a skeleton 3.1 whatsnew document.
diff --git a/Doc/whatsnew/index.rst b/Doc/whatsnew/index.rst
index 0dc55d8..4d2bf3f 100644
--- a/Doc/whatsnew/index.rst
+++ b/Doc/whatsnew/index.rst
@@ -11,6 +11,7 @@
 .. toctree::
    :maxdepth: 2
 
+   3.1.rst
    3.0.rst
    2.7.rst
    2.6.rst