New section in Wiki - Please review

[jamacku]

I wanted to propose a new section for the Wiki page, but I wasn't sure how to do it properly, so I did it via web UI. When I hit save, my changes were reflected immediately.

Relevant change: https://github.com/koalaman/shellcheck/wiki/GitHub-Actions + Updated Sidebar

I don't know what is the process for extending Wiki pages, please review those changes. Thank you.