Add name to example 'nix-channel --add' command on latest channel page

[dgroenewegen]

It would be better if the example 'nix-channel --add' command on latest channel page suggests adding a name, to avoid having channels with name 'latest' and overriding any other such 'latest' channels. E.g. on http://hydra.nixos.org/project/spoofax/channel/latest

instead of

nix-channel --add http://hydra.nixos.org/project/spoofax/channel/latest

show

nix-channel --add http://hydra.nixos.org/project/spoofax/channel/latest spoofax-latest