Add documentation for all the folders

[Thanveerahmedshaik]

📘 Documentation Task

We need to add README.md documentation to each folder in this repository.
Each README should include:

• Overview of the folder
• Quick run instructions
• Table of problems/algorithms with file links, time/space complexity
• Notes/gotchas
• Resources (if relevant)

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📂 Folders to document

• Math
• Hashing
• Recursion
• Sorting
• Lists
• Leetcode

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✅ Acceptance Criteria

• Every folder has a README.md file
• Each file is consistent with the template format
• At least one algorithm/problem listed per folder
• Linked in the root README.md