Complete Merge Sort Note

[Nilesh091]

Fixes #74

Short description of what this resolves:

Adds a comprehensive and well-structured explanation of the Merge Sort algorithm, including time and space complexity, advantages, disadvantages, interview points, and usage scenarios, to improve clarity and learning experience.

What Changes proposed in this pull request:

• Added detailed Time and Space Complexity analysis for Merge Sort
• Included advantages, disadvantages, and interview quick points
• Added a concise summary and usage guidelines
• Improved documentation readability and educational value

Checklist

• Added description of change
• Added file name matches File name guidelines
• Added code examples, test must pass
• Added documentation so that the program is self-explanatory and educational.
• Relevant documentation/comments is changed or added
• PR title follows semantic commit guidelines
• Search previous suggestions before making a new one, as yours may be a duplicate.
• I acknowledge that all my contributions will be made under the project's license.

Notes:
This PR improves Merge Sort documentation quality, making it more beginner-friendly and interview-oriented.