Add support for contributors

[NateWr]

I noticed that some guides include contributor attribution, such as https://docs.pkp.sfu.ca/google-scholar/en/. It should be easy to add frontmatter that allows us to identify contributors:

---
contributors: Kate Shuttleworth, Emily Zheng, Monica Westin, Roger Gillis, Patricia Manghais
---

That would then allow us to markup the contributor information semantically, and add appropriate metadata. The use of a blockquote will be confusing for people using assistive technology.