[cpp-threads] Web site updated

[Peter Dimov]

Boehm, Hans wrote:

> There is currently no statement in the specification to ensure that
> "raw" atomic accesses become visible elsewhere "promptly", for example
> that read accesses should not be cached in a register.  I expect it
> would be hard to define that precisely, but it may be good to add a
> note to that effect in the documentation for the atomics library.

We probably want to say that it becomes visible "eventually", if not 
"promptly".