[DOCS] Improve README and CONTRIBUTING GUIDE + Add Broken Link check

[dansysanalyst]

⚡ PowerGrid - Pull Request

Welcome and thank you for your interest in contributing to our project!. You must use this template to submit a Pull Request or it will not be accepted.

---

Motivation

• [ ] Bug fix
• [x] Enhancement
• [ ] New feature
• [ ] Breaking change

Description

This Pull Reque improves the README and CONTRIBUTING GUIDE and brings Lychee in GitHub Actions to check for broken links in *.md files.

Documentation

This PR requires Documentation update?

• [ ] Yes
• [x] No
• [ ] I have already submitted a Documentation pull request.