Update inaccessible external links in contributing documentation

[hmke228]

Description

Updates two inaccessible external links in contributing.md:

1. LUFA link changed from https://www.fourwalledcubicle.com/LUFA.php to https://github.com/abcminiuser/lufa per guidance by @drashna
2. http://www.catb.org/esr/faqs/smart-questions.html changed to GitHub mirror: https://github.com/selfteaching/How-To-Ask-Questions-The-Smart-Way

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

• Related to Inaccessible external links in "Contributing" documentation #26368
• I am aware of existing PR docs: fix dead links in contributing guide #26370, which also addresses these broken links by replacing the LUFA link and removing the catb.org link. This PR proposes keeping a reference to "How To Ask Questions The Smart Way" by replacing the dead URL with an available GitHub mirror. I thought I would offer this as an alternate approach in case preserving access to the resource is preferred.

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).