Import asciidoc hdlist styling

Certain Fedora Docs documents (the fonts packaging policy, for example) make heavy use of what asciidoc terms horizontal description lists. However, none of the styling for such lists is present in the doc.css file.

This MR imports the hdlist styling from the default asciidoc CSS into doc.css.

Without it, the lists render... badly.

(Left column should be bold, valign: top, and separated from right column by some margin spacing padding.)