Add Dockerfile and docs on how to run with docker when node10 isn't available

[Ramblurr]

• Add Dockerfile suitable for running multimeter locally
• Add docs to README regarding node 10 dependency and how to use docker.

[SystemParadox]

I think this is unnecessary. We just need to get screeps-api to update their bufferutil dependency. It actually still seems to work anyway - see my comments on https://github.com/screepers/screeps-multimeter/issues/33.