Add intros to REST API pages

[ethanpalm]

What article on docs.github.com is affected?

• "Git database"
• "Gitignore"
• "Interactions"
• "Issues"
• "Licenses"

What part(s) of the article would you like to see updated?

Each of these articles needs an intro to help orient users to the content on the page and what each API can be used for. Intros should be one sentence long and define what the feature is.

For "Git database" and "Licenses," you can cut and paste the first sentences in the articles for the intros.

For "Gitignore," "Interactions," and "Issues" you will need to write new intros.

For more information about writing intros, see:

• Information about writing intros in the GitHub docs content model
• Information about the intro frontmatter property in the GitHub Docs content directory README

Additional information

This issue is for the Campus Experts + Docs program and not currently available for contributors outside the program to work on.

[codewithdev]

Would like to work on this. :)

[ramyaparimi]

@codewithdev Thank you for willing to work on this ✨ feel free to open a PR whenever ready 👍