This applies to Categories, tags, etc.
My template uses a taxonomy called Series (or stories) and I needed to add more information to it.
The solution I found, which includes some posts here in the forum, was to use the Data folder.
There is a TOML file at data/series/ with the same name as the series. Like story-name.toml. After which I cycle through the information to make sure it matches.
TOML data file
slug = "uxlx15"
name = "UX Lx 2015"
description = "User Experience Lisbon"
and then the template at terms.html
{{ range $key, $value := .Site.Taxonomies.series }}
{{ range $.Site.Data.series }}
{{ if eq $key .slug }}
<article class="mini-post stories">
<header>
<p>{{ .description }}</p>
</header>
<a href="{{ $baseurl }}series/{{ $key | urlize }}/" class="image mini-featured-image" style="background-image: url('{{ $baseurl }}series/{{ $key | urlize }}/{{ $key | urlize }}_header.jpg');"><h3>{{ .name }}</h3></a>
</article>
{{end}}
{{end}}
{{ end }}
There may be a more elegant way to match the Series to the data file,but for the time being the above works just fine.