Add Docker image usage documentation

[jerluc]

Currently, the README only spells out how to install/use tilenol from source, but ideally most users would only be using tagged binaries. IMO we should update our README to:

• [x] Add a new "Docker" section to "Usage"
• [x] Add descriptions of Docker image tag conventions (e.g. devel vs. latest)
• [x] Add actual usage examples for the Docker image
• [x] Add Docker Hub link(s): https://hub.docker.com/repository/docker/stationa/tilenol
  • [x] Update Docker Hub's "Readme" section with image usage

Moved the below to #32:

~Optionally, we could also go a bit further by:~

• [ ] ~Connecting Docker Hub and Github to sync Docker Hub's "Readme" section~
• [ ] ~Use Github's new "package" feature to publish Docker images~
• [ ] ~Implement #32 to auto-publish new images and sync to our repo somehow~

[jerluc]

Closed in 1c09fc5