The exports.5 man page is a bit of a monster.
One place of common confusion is the use of
the "V4:" line(s) for defining the location of the
root of the NFSv4 export subtree.

This patch adds a paragraph in an attempt to
clarify this.

Although I am trying to avoid any attempt at
a major re-write of this man page, simple
suggestions for improvement (such as making
it into more paragraphs or ??) will be entertained.