Add link to dockerfile, if desired

[Josh Bothun]

Hello! Thanks for your work on this tool, its been really helpful for me.

I created a dockerfile which installs java, .NET SDK, graphviz, plantUML and your tool, to make it easier to run a one-off on C# code without needing to setup any dependencies.

https://hub.docker.com/repository/docker/minism/plantuml-csharp

Feel free to link to this somewhere on your README if you'd like.