Fix Docker instructions / port mapping

[pawelzar]

I noticed that the Docker Hub instructions for running Swagger Editor locally are misleading.

The current instruction:

docker run -d -p 80:8080 docker.swagger.io/swaggerapi/swagger-editor

maps host port 80 to container port 8080. However, Swagger Editor’s nginx actually serves the editor on port 80 inside the container - there is no custom nginx configuration to listen on 8080.

This PR:

• Updates the EXPOSE instruction in the Dockerfile to match the actual container port.
• Fixes the docker run command in README.md to correctly map host port to container port 80.

it would be great to update the Docker Hub instructions as well to match this fix. I also noticed that the instruction has a broken link to Importing your OpenAPI document.