Expose Documentation in Docker Container

[morgabm]

Is your feature request related to a problem? Please describe.
Some use cases for the docker container involve offline usage. I must then go to https://plantuml.com/ for documentation.

Describe the solution you'd like
I would like syntax reference/documentation available within the docker container.

Describe alternatives you've considered
Using the web hosted documentation

I have looked and not seen any documentation if this is already a thing.