Added stub release notes for 5.1.3.

docs/releases/5.1.3.txt

@@ -0,0 +1,12 @@
+==========================
+Django 5.1.3 release notes
+==========================
+
+*Expected November 5, 2024*
+
+Django 5.1.3 fixes several bugs in 5.1.2.
+
+Bugfixes
+========
+
+* ...

docs/releases/index.txt

@@ -32,6 +32,7 @@ versions of the documentation contain the release notes for any later releases.
 .. toctree::
    :maxdepth: 1
 
+   5.1.3
    5.1.2
    5.1.1
    5.1