Add CI for Docker

[egbaydarov]

I have set up a simple CI for automatically updating the image in the public Docker Hub repository: https://hub.docker.com/r/baydarov/draggan. You can verify that the action is working perfectly in my fork.

To incorporate this into your repository, you need to follow several steps:

1. Create an account on https://hub.docker.com.
2. In your repository settings, create secrets (DOCKER_USERNAME and DOCKER_PASSWORD) and provide the exact username and password (or use a token found in DockerHub -> Profile -> Security) of your newly created Docker Hub account.
3. Share your Docker Hub username with me so I can grant you permission to push into the baydarov/draggan repo.
4. Merge the branch and verify that the CI is working properly.