Updated index.md and added sorting-algorithms.md under issue #191

[Yatharth31]

PR Description

Added "Sorting algorithms (Bubble, selection, quick and merge sort)" and updated index.md accordingly.

Related Issues

• Closes #190

Checklist

• [x] I have gone through the contributing guide
• [x] I have updated my branch and synced it with project main branch before making this PR

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I declare that:

1. The content I am submitting is original and has not been plagiarized.
2. No portion of the work has been copied from any other source without proper attribution.
3. The work has been checked for plagiarism, and I assure its authenticity.

I understand that any violation of this undertaking may have legal consequences that I will bear and could result in the withdrawal of any recognition associated with the work.

• [x] I Agree