Link also the manual in a channel

[domenkozar]

Each channel should also have a link to the manual at https://d3g5gsiof5omrk.cloudfront.net/nixpkgs/nixpkgs-17.03pre94051.cbec6a3

[domenkozar]

This was removed in d3d33d5#diff-682bf482f6dd273f1c3c49afd99b4660L77, @edolstra was that on purpose?

[JohnAZoidberg]

I think it'd be nice to have the manual referring to that specific version linked in the channel. Should we add it back?