Minor usability update

Changed

• in devcontainer, load Pylance VS Code extension later as the required Pyhton extension does not always load quickly enough.
• alt text for project intro image
• Added empty line after 2nd 'div' in About the Project. This is required to show links correctly.
• Set default value to false (as opposed to simple) for customized_install install question in copier.yaml

Removed

• README-reference.md from the generated scaffolding.