Document requirements for `ci/circleci: lint-git` and CHANGELOG in Developer Guide

[JackAtOmenApps]

Feature Request

The Contribute section of the Developer Guide does not provide any information about the Circle-CI requirements for updates to CHANGELOG and the syntax for git commit titles and body. This should be clearly explained so that contributors know what is expected.

[JackAtOmenApps]

I tried to create a couple PRs (#53 and #54), but I cannot get them to pass the ci/circleci: lint-git check.

Edit: Updated docs in #56 to describe the requirements for git commit messages and the CHANGELOG.