docs: move pull request requirements instructions into a comment (#551)

Author: zimeg

.github/pull_request_template.md

@@ -2,7 +2,7 @@
 
 Describe the goal of this PR. Mention any related Issue numbers.
 
-### Requirements (place an `x` in each `[ ]`)
+### Requirements <!-- Place an `x` in each `[ ]` -->
 
-* [ ] I've read and understood the [Contributing Guidelines](https://github.com/slackapi/slack-github-action/blob/main/.github/contributing.md) and have done my best effort to follow them.
-* [ ] I've read and agree to the [Code of Conduct](https://slackhq.github.io/code-of-conduct).
+- [ ] I've read and understood the [Contributing Guidelines](https://github.com/slackapi/slack-github-action/blob/main/.github/contributing.md) and have done my best effort to follow them.
+- [ ] I've read and agree to the [Code of Conduct](https://slackhq.github.io/code-of-conduct).