Add changelog / release notes for 2.9

CHANGELOG.txt

@@ -1,6 +1,12 @@
 Changelog
 =========
 
+2.9 (xx.xx.xxxx) - IN DEVELOPMENT
+~~~~~~~~~~~~~~~~
+
+ * ...
+
+
 2.8 (xx.xx.xxxx) - IN DEVELOPMENT
 ~~~~~~~~~~~~~~~~
 

docs/releases/2.9.rst

@@ -0,0 +1,28 @@
+==========================================
+Wagtail 2.9 release notes - IN DEVELOPMENT
+==========================================
+
+.. contents::
+    :local:
+    :depth: 1
+
+
+What's new
+==========
+
+
+Other features
+~~~~~~~~~~~~~~
+
+ * ...
+
+
+Bug fixes
+~~~~~~~~~
+
+ * ...
+
+
+Upgrade considerations
+======================
+

docs/releases/index.rst

@@ -5,6 +5,7 @@ Release notes
    :maxdepth: 1
 
    upgrading
+   2.9
    2.8
    2.7.1
    2.7

docs/releases/upgrading.rst

@@ -133,3 +133,5 @@ The compatible versions of Django and Python for each Wagtail release are:
 +-------------------+------------------------------+-----------------------------+
 | 2.8               | 2.1, 2.2, 3.0                | 3.5, 3.6, 3.7, 3.8          |
 +-------------------+------------------------------+-----------------------------+
+| 2.9               | 2.1, 2.2, 3.0                | 3.5, 3.6, 3.7, 3.8          |
++-------------------+------------------------------+-----------------------------+