[relax-ng] clarfication re. NIST hosting

I was mistaken when I said that NIST-hosted telecons can't provide a
toll-free number for callers from outside the US.

I asked the telecon folks at NIST and found out that toll-free access is
available to non-US participants as long as NIST knows their names in
advance.

Joshua Lubell, NIST
100 Bureau Drive, Stop 8263
Gaithersburg MD 20899-8263 USA
(301) 975-3563