Explain that a "list" means "of lines" not of YAML

[kousu]

Why:

If I try

    - name: caching
      uses: actions/cache@v2
      with:
        path:
          - ~/.cache
        key: build-${{ github.ref }}
        restore-keys: |
          build-

I just get an unexplained "Startup Failure": https://github.com/spine-generic/data-multi-subject/actions/runs/742876119. Switching to a YAML multiline string

    - name: caching
      uses: actions/cache@v2
      with:
        path: |
          ~/.cache
        key: build-${{ github.ref }}
        restore-keys: |
          build-

works: https://github.com/spine-generic/data-multi-subject/actions/runs/742878382

What's being changed:

Check off the following:

• I have reviewed my changes in staging. (look for the deploy-to-heroku link in your pull request, then click View deployment)
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[welcome]

Thanks for opening this pull request! A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.

[janiceilene]

@kousu Thanks so much for opening a PR! I'll get this triaged for review ⚡

[martin389]

Changes in this PR

Article in staging	Changes
“Input parameters for the cache action”	Clarifies how to define multiple paths in path. Adds example.

Tests

All tests are passing! 🍏

[martin389]

Thanks for the PR @kousu 🎊 This is really helpful!

I've also added an example codeblock to the section, because I noticed we don't demonstrate multiple paths in the article.
Added the multiple path example from https://docs.github.com/en/actions/guides/building-and-testing-java-with-gradle#caching-dependencies

[martin389]

Added some edits based on peer review

[github-actions]

Thanks very much for contributing! Your pull request has been merged 🎉 You should see your changes appear on the site in approximately 24 hours. If you're looking for your next contribution, check out our help wanted issues ⚡