Add option --host for hem server to documentation.

[usamec]

I cannot find this option anywhere and spent like hour finding out how to run this on nonlocalhost port.

[aeischeid]

good point. Hem could really use some documentation love.

[cengebretson]

Yeah, its definitely time to give hem some love with updates and better documentation. I'm hoping (fingers crossed) that the next couple of weeks I'll be able to get some free time to clean things up.

[aeischeid]

I am goign to work on docs, though I think we have this minor bit maybe handled