Docs: Reword PR template

[vanessayuenn]

What I did

Edited the PR template. More specifically, I:

• Moved some sections around to clarify things
• Made the testing section mandatory
• Added description for each PR label

How to test

No test necessary! Just 👀

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "build", "documentation", "maintenance", "dependencies", "other"]

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=<PR_NUMBER>

[yannbf]

This looks really good! I just wonder about the wording for folks who make documentation changes only, and might be confused if they have to tick the checkboxes. Can you add something about documentation PRs?

[kylegach]

I love that these are briefly described now! ❤️

Are these in any particular order? I suggest either most-common first or alphabetical (keeping the non-changelog impacting ones grouped together, as you've done).

[vanessayuenn]

This looks really good! I just wonder about the wording for folks who make documentation changes only, and might be confused if they have to tick the checkboxes. Can you add something about documentation PRs?

I thought about it but ultimately decided it's simpler to offer one protocol instead of "if code changes, do this, if docs changes, do something else". Docs-only contributions can just not check any of the checkboxes, like how it is currently.