Add release notes page for version 0.9.0

Patrole 0.9.0 has been released.
This commit adds a new page for 0.9.0 release notes.

Change-Id: I0802b5c934402b8d25113cea5eb55ab1f9494038
diff --git a/releasenotes/source/index.rst b/releasenotes/source/index.rst
index 32f74ec..b3922e6 100644
--- a/releasenotes/source/index.rst
+++ b/releasenotes/source/index.rst
@@ -6,6 +6,7 @@
    :maxdepth: 1
 
    unreleased
+   v0.9.0
    v0.8.0
    v0.7.0
    v0.6.0