Re: [PATCH v6 5/4] copy_file_range.2: New page documenting copy_file_range()

It's probably worth mentioning the sparse expansion caveat
in the docs, as it's important and not obvious.

I.E. copy_file_range() could be called from, but would
still benefit from a user space app using a SEEK_{HOLE,DATA} loop.

thanks,
Pádraig.