Comment on the pull request with the expected output from the nop

## Prerequisites:

* Is the functionality available in the GitHub UI? If so, please provide a link to information about the feature.
n/a

* Is the functionality available through the GitHub API? If the functionality is available, please provide links to the
API documentation (https://developer.github.com/v3/) as well as the Octokit documentation (https://octokit.github.io/).
n/a
* If the functionality is not yet available in the API, it would be helpful if you
contacted support (https://support.github.com/) or posted in the Community Forum (https://github.community/). Please
include a link to the forum post if you create one or a copy of the response from support.
n/a
## New Feature

Please describe the desired new functionality:

I've yet to fully experiment with this, but the README suggests that safe-settings runs a dry-run for the changes on a PR in the admin repo https://github.com/github/safe-settings#pull-request-workflow

Looking at the code https://github.com/github/safe-settings/blob/ec8777254d5e9508bfb0946f021f9a52d6cdabcd/index.js#L187 it would appear that the result of the check is simply output to stdout.

It would be more useful if a comment was left on the PR such that a person could review the changes that the app will make to make sure there are no unexpected changes.