fix: markdown formatting correction in CONTRIBUTING.md file

[superiorsd10]

Description

I've corrected the markdown formatting in the CONTRIBUTING.md file to improve readability and usability. The mistake was related to the markdown link syntax.

Specific Changes:

• Corrected the formatting of the link to compatible Flutter SDK versions.
• Replaced inline code formatting with a standard link format.
• Ensured that the URL in the link is correctly formatted.

These changes make the document more user-friendly and help users access the linked resource without confusion.

Resolves #822

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore