We need a release notes page to show notes for unreleased versions by
scanning the "current" branch. This ensures that notes files cannot be
merged if they break the releasenotes job.
unreleased.rst file was missed in main commit:
I8ffe53af594150529c325814cf55812268193172
This patch fixes it.
Change-Id: Ib324a69366437f3df6cfffabfde0c1a8d35c22eb