Add release notes page for v0.4.0

Patrole 0.4.0 has been released [1].
This commit adds a new page for v0.4.0 release notes.

[1] https://review.openstack.org/#/c/592277/

Change-Id: I98519d5f4ff788fee485e735f4c284ea1dd00c28
2 files changed