Reorganized and clarrified the Holland backup-set config docs.

Re-arranged a few paragraphs to flow better, reworded things that
didn't make as much sense, provided better examples of the hooks.
"by default" seems to imply the backupsets location is configurable, however this isn't currently the case in holland 1.0.X.   ./backupsets/ is expected to be relative to the required holland.conf main config file.