Update Dockerfile

[westonmyers]

Image built based on Dockerfile in repo would not bring up properly. Bringing inline with documentation.

I suppose that the project could also use an update on the wiki to include using mooncord in a container. I may push in something for that later.

[eliteSchwein]

Hey there, thanks for the PR.

i oversaw the PR, sorry about that. Looks good to me. Also about the wiki, i will move to gitbook soon, because the github wiki is kinda limited...