Put data about your authors in data/authors.yml
.
An author entry looks like this:
siteAdmin:
name: Site Admin
slug: site-admin
imageUrl: /assets/images/kyoto.jpg
twitterUrl: https://twitter.com
facebookUrl: https://facebook.com
bio: This is my personal little blurb
Authors must have a name and slug. The object key is how your reference the object in post metadata and the author slug is how the author appears as part of URLs.
Some themes respect other things such as imageUrl, etc.