Add multiarch support

[werdnum]

Looks like this image only works for amd64 / x86_64. Would be great to have a multi-arch docker image (as explained here).

Looks like the Dockerfile needs a few adjustments too in the URLs and paths.

[werdnum]

Here's a commit that makes it work on Raspberry Pi: werdnum@64a3e73

[wlatic]

Used this and it worked great!

[webash]

+1 to 'official' multi-arch in the main repo, but for now I'll borrow @werdnum 's modifications. Thanks!

[pirate]

#12