[wwwdocs] Release notes for SVE

[Gerald Pfeifer]

On Tue, 20 Mar 2018, Richard Sandiford wrote:
> I thought I had to use the passive tense because all the other bullet
> points in that section do, but I guess in some ways "GCC now supports..."
> would avoid the shift in subject.

It's a good point, actually.  Many style guides actually recommend
to avoid passive tense, and it may be worth going through the release
notes and one point and seeing what we can adjust.  In any case, it's
definitely fine to use active tense.

Gerald