docs/168885: man page for find(1) fails to describe the -depth option

[Ronald F. Guilmette]

Regarding this PR:

http://www.freebsd.org/cgi/query-pr.cgi?pr=168885

I noticed after I had filed it that actually, the -d option for find(1) is
``documented'' (for some value of ``documented'') in _two_ different locations
within the find(1) man page, i.e. under the DESCRIPTION heading, and also under
the PRIMARIES heading.

In the first location, a full and complete description of the function of the
-d option is in fact given.  However in the second location, virtually nothing
is said about the functionality of -d, and there isn't even a reference
telling the reader to look for documentation of the -d option higher up
within the man page.