improvements to bot warning message

[ianstormtaylor]

Similarly to #27, right now the changeset warning message looks like:

But I think it could be simplified and more clear as:

Markdown for the example.

⚠️ No changeset detected. 5461a06f94cddce0b573f41948ba79b6117c4c96

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

If you add a changeset this comment will update to reflect it.

• Not sure what this means? Click here to learn what changesets are.
• Want to add a changeset? Click here to add another changeset to this PR.