[wwwdocs][patch] Document the change of default vector size for ARM NEON

[Gerald Pfeifer]

On Tue, 16 Aug 2011, Ira Rosen wrote:
> The first part was already reviewed several months ago, but I am
> resubmitting it along with -mvectorize-with-neon-double documentation.
> 
> OK to commit?

Looks good, thank you.

Gerald