Update setup-linux.sh

Install vibe.d on /usr/local/share/vibe.d, create a Menu entry for the new vibe.d documentation, update "vibe.conf" to the new "user/group" fields, include a help screen, use "www-data" as "user/group" if in Debian like system.
Merge pull request #150 from jordisayol/patch-1

Update setup-linux.sh