DOC: Changelog skeleton

Changelog

@@ -24,6 +24,24 @@ Gerhard (SG), Eric Larson (EL), Yaroslav Halchenko (YOH) and Chris Cheng (CC).
 
 References like "pr/298" refer to github pull request numbers.
 
+2.4.0 (Monday 25 March 2019)
+============================
+
+New features
+------------
+
+Enhancements
+------------
+
+Bug fixes
+---------
+
+Maintenance
+-----------
+
+API changes and deprecations
+----------------------------
+
 2.3.3 (Wednesday 16 January 2019)
 =================================