Add dockerfile

This MR

• adds a Dockerfile to the repo
• defines a CI/CD config to build and store the Docker image based on said file in this repo's container registry
• extends the README

To test it:

• check out this branch
• build the Docker image (docker build -t eupt-website .)
• run the image (docker run --rm -p 8080:80 eupt-website)
• go to http://localhost:8080 and check if everything is running as expected