Add more description and clarification about the -depth and -d options in both places where they are mentioned in find(1).
Add more description and clarification about the -depth and -d options in
both places where they are mentioned in find(1).

Discussed with:	dougb
PR:		docs/168885
Reported by:	Ronald F. Guilmette (rfg at tristatelogic dot com)
Approved by:	gabor (mentor)
MFC after:	3 days

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