There’s a sample config.toml file in the root of the indigo theme directory (config.toml.example); copy it to the root of your Hugo site, and rename it to config.tomlafter you’ve made a backup of your current config.toml file (if any).
Set up the parameters in the config file, especially those in the social and params.indieWeb section. Social identifiers that you leave out will not be added to the footer of the site.
You can configure the theme to show info about the author; by default, this information is shown; if you’d prefer to leave it out, set ShowBio to false.
Indigo will look for custom CSS in <YOUR_HUGO_SITE>/static/css/custom.css. This will let you add/override styling to your heart’s content, while making it easy to keep Indigo up-to-date. See it in action on angelostavrow.com.
You can add a line to your config.toml file to set this theme as the default:
theme = "indigo"
Or, if you use config.yaml:
Indigo IndieWeb Features
A thorough writeup of the theme has been graciously written by @infominer33.