Replace or remove deadlinks & inactive badges in README

[brnnnfx]

Overview

• Updates URLs for links where the content is still available but the link is outdated

• Removes deadlinks and inactive badges in the README if there are no known suitable replacements

Testing recommendations

Navigate to all links & review the content on the linked pages to ensure readers will be directed to what they need

GitHub issue number

This resolves issue #289 (Several README links direct to a 404 page or are inactive)

Checklist

• [X] Code is written and works correctly;
• [ ] Changes are covered by tests;
• [ ] Documentation reflects the changes;

📝 Note - The latter two checkboxes are un-checked because these changes are made to Markdown documentation. There are no tests and this document is documentation itself.

[brnnnfx]

Hi @glynnbird given your suggestion, is there anything more you would want to see from this change?