Docker for local development

[nirname]

I'd like to contribute to Mermaid, but this is rather inconvenient for me to install everything locally. I prefer to launch everything in container system, that currently is Docker. Being rather a full-stack developer I am forced to install many different versions, because there are plenty of things to support. And when a team member joins, I prefer his instructions to be so simple that his grandmother could follow it. Whereas in that very case it simplifies nothing (even a little of opposite), but had it been setup within container it would have been more encapsulated thus I could more easily dispose of unneeded installations.

Seems, that this PR is not following rules, because it does not address any issue, but please, skim through it to grasp the idea of how it may look like