Added security release note stubs.

docs/releases/1.4.21.txt

+===========================
+Django 1.4.21 release notes
+===========================
+
+*July 8, 2015*
+
+Django 1.4.21 fixes several security issues in 1.4.20.

docs/releases/1.7.9.txt

@@ -2,9 +2,12 @@
 Django 1.7.9 release notes
 ==========================
 
-*Under development*
+*July 8, 2015*
 
-Django 1.7.9 fixes several bugs in 1.7.8.
+Django 1.7.9 fixes several security issues and bugs in 1.7.8.
+
+Bugfixes
+========
 
 * Prevented the loss of ``null``/``not null`` column properties during field
   renaming of MySQL databases (:ticket:`24817`).

docs/releases/1.8.3.txt

@@ -2,9 +2,9 @@
 Django 1.8.3 release notes
 ==========================
 
-*Under development*
+*July 8, 2015*
 
-Django 1.8.3 fixes several bugs in 1.8.2.
+Django 1.8.3 fixes several security issues and bugs in 1.8.2.
 
 Also, ``django.utils.deprecation.RemovedInDjango20Warning`` was renamed to
 ``RemovedInDjango110Warning`` as the version roadmap was revised to 1.9, 1.10,

docs/releases/index.txt

@@ -95,6 +95,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   1.4.21
    1.4.20
    1.4.19
    1.4.18