Better release notes

[laverya]

Expected behavior

The contents of the Description for the Changelog portion of PRs are included in the release notes

Actual behavior

They are not, instead all commit messages are.

Information

• Ship version: Master as of https://github.com/replicatedhq/ship/commit/b94c437e2007262a2ca502eb568d415121da0d16

Steps to reproduce the behavior

1. Make a release by pushing a new semver tag
2. Look at the releases list and observe the lack of messages from the Description for the Changelog portion of the included PRs.