Contributors list for each documentation page.

[resir014]

This will be a useful feature to have. Each contributors to the page would be credited and their avatars will show up somewhere in the docs (a la Microsoft documentation).

Tech breakdown

In the documentation page, we'll add a new contributors frontmatter which is an array of all GitHub usernames of people who have contributed.

contributors: ["user1", "user2", ...]

Then using gatsby-source-github and Gatsby's mapping feature, we map the above usernames to the GitHub user object so we can call them through GraphQL on the page template.