[New Feature]: Include instructions for using pre-built container from GHCR

[whatnick]

Checked for duplicates

Yes - I've already checked

Alternatives considered

Yes - and alternatives don't suffice

Related problems

README instructions point to building from Docker file which can take a while and depend on users local environment somewhat.

Describe the feature request

The repository CI builds a GHCR container and this can be directly pulled to accelerate setup and usage. Happy to make PR to this effect.

• A pointer to creating GHCR token
• Pulling the image via docker pull ghcr.io/isce-framework/dolphin:latest
• Running the image and mounting volumes to perform basic processing.