Added stub release notes for 2.2.4.

docs/releases/2.2.4.txt

@@ -0,0 +1,12 @@
+==========================
+Django 2.2.4 release notes
+==========================
+
+*Expected August 1, 2019*
+
+Django 2.2.4 fixes several bugs in 2.2.3.
+
+Bugfixes
+========
+
+* ...

docs/releases/index.txt

@@ -32,6 +32,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   2.2.4
    2.2.3
    2.2.2
    2.2.1