Add new release note sections for 1.10

CHANGELOG.txt

@@ -1,6 +1,10 @@
 Changelog
 =========
 
+1.10 (xx.xx.xxxx) - IN DEVELOPMENT
+~~~~~~~~~~~~~~~~~
+
+
 1.9 (xx.xx.xxxx) - IN DEVELOPMENT
 ~~~~~~~~~~~~~~~~
 

docs/releases/1.10.rst

@@ -0,0 +1,23 @@
+===========================================
+Wagtail 1.10 release notes - IN DEVELOPMENT
+===========================================
+
+.. contents::
+    :local:
+    :depth: 1
+
+
+What's new
+==========
+
+
+Other features
+~~~~~~~~~~~~~~
+
+
+Bug fixes
+~~~~~~~~~
+
+
+Upgrade considerations
+======================

docs/releases/index.rst

@@ -4,6 +4,7 @@ Release notes
 .. toctree::
    :maxdepth: 1
 
+   1.10
    1.9
    1.8.1
    1.8