doc: improve maintainability and readability of collaborator list

Line wrapping the contributors list in the markdown makes it harder to read, as is evidenced by the frequent mistakes made when updating the list where a person inserts their name in the middle of another collaborator's entry. Put everything on one line to keep it readable and maintainable.

Additionally, make it easier to understand in raw markdown by removing the GitHub link. In the GitHub interface, that link will be provided automatically. In raw markdown, it's a lot easier to read and understand without it and people will be able to figure out the link to the person's GitHub profile if they really want it.

Checklist

• documentation is changed or added
• commit message follows commit guidelines