Add intros for articles on commits

[FlyteWizard]

Why:

Closes #6797

What's being changed:

Added intro for "Comparing commits" article. This intro is pulled from the top section of the text on the article.

You can compare the state of your repository across branches, tags, commits, forks, and dates.

Added intro for "Differences between commit views" article.

You can sometimes observe differences in commit history depending on the chosen viewing method.

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 completed the self-review checklist.

Writer impact (This section is for GitHub staff members only):

• This pull request impacts the contribution experience
  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (e.g. a "before and after video")

[janiceilene]

🎉 Thanks for opening another PR @FlyteWizard 🎉 I'll get this triaged for review ✨

[guntrip]

Hi @FlyteWizard! Thanks so much for this contribution ✨

I had one suggested change, which I'll apply now, and then get this merged!

[github-actions]

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