Added robots meta tags in html head in case ZeroBin is not installed at root.

From
https://github.com/elrido/ZeroBin/commit/2470871e709a227c72fe664143672b520ec8c62e
Allow discovery

Patch from
https://github.com/ic0nic/ZeroBin/commit/50d4fb9bf36ed154792e8a7d4d7d444f59581c74