Log "additional sections"

[wbamberg]

In stumptown we have:

• named prose sections that must be present (e.g. "Short description")
• named prose sections that may be present (e.g. "Accessibility concerns")
• additional prose sections that may have any names (e.g. "Supported image formats")

We would like the tools to log the names of additional sections, partly so we can see additional sections that are very often included and should perhaps be promoted to named sections.

See also #14 (comment).