To easier the trial, add docker image

[arukiidou]

For users unfamiliar in Rust, getting started with svgbob takes a bit of work.

To easier the trial, It would be nice to have a docker image.
language-independent docker imege makes it much easier to use with CI.
(e.g. gitlab, jenkins)

Until an official image registry is created, the following unofficial image registry has been prepared.
If possible, an official image registry would be better.

docker hub unofficial image

https://hub.docker.com/r/arukiidou/svgbob_cli