Small changelog updates prior to next release.

[webframp]

---

Pull Request Checklist

Is this in reference to an existing issue?

Not quite. Follow up to discussion in https://github.com/sensu/sensu-go-chef/pull/66#issuecomment-543934603

General

• [X] Update Changelog following the conventions laid out here

Purpose

Update the CHANGELOG with any important information we’ve missed before the next release.

[webframp]

@majormoses You can check my work here in case I forgot something.