make call info for groups an include

[glenrobson]

From: IIIF/api#1002

@srabun You might consider making this an 'include'. See, e.g., at the end of this section. The line {% include copyright.md %} corresponds to the file source/_includes/copyright.md, which gets copied in when the site is built. It keeps you from having to maintain the info in multiple places. You could make something like call_info.md and do similar.