chore: document format of expected comment patterns that contribute to the score

[zimeg]

Problematic comments. Comments that include "TODO", "HACK" and "FIXME" tend to signal that some corners were cut and shortcuts taken, which may negatively impact the long-term health of a project.

https://github.com/slackapi/slack-health-score/blob/02ba2a5c9e9887e03cfc8933acbc6153ff0ba268/README.md

📝 It's not so clear if "tagged" comments are supported in the current version of this action, but this behavior should be noted with what's supported:

• TODO
• TODO(semver:major)