Convert nfsd-admin-interfaces to ReST and move it into admin-guide.
Content remains mostly untouched.
Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
Link: https://lore.kernel.org/r/d471305e9c96dec38f18d2ff816fca2269a88e29.1578697871.git.dwlsalmeida@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>