[Systems] doc.sl.o instead of api.sl.o

[Aleksey Lim]

Hi all,

We might have (as we already do) not only glucose documentation within
SL, thus would be useful to have doc.sugarlabs.org instead
api.sugarlabs.org (but having http redirect).

If people agree, please add new DNS record and I will add http redirect.

-- 
Aleksey