Fix: Add MDN Strict Inequality Link

[Manish-Giri]

Pre-Submission Checklist

• Your pull request targets the staging branch of FreeCodeCamp.
• Branch starts with either fix/, feature/, or translate/ (e.g. fix/signin-issue)
• You have only one commit (if not, squash them into one commit).
• All new and existing tests pass the command npm test. Use git commit --amend to amend any fixes.

Type of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)
• Add new translation (feature adding new translations)

Checklist:

• Tested changes locally.
• Closes currently open issue (replace XXXX with an issue no): Closes === is not opposite of !== #11763

Description

Modified challenge instruction as recommended. Added an MDN link about strict inequality to the challenge.

I'm not completely sure if I've referenced the MDN link from the MDN Links file the right way in the challenge. Please review the PR and let me know if any changes are required! Thanks!

closes #11763

[dhcodes]

Tested and LGTM! Now to get those MDN links working...
Thanks for contributing @Manish-Giri 👍 🌮 🎉