[Docs] Improve README + Add Contribution Guidelines

[NhanPhamThanh-IT]

Description

Hi, I would like to propose improvements to the repository’s documentation to make it more contributor-friendly and easier to understand for newcomers.

Suggested Improvements

1. Enhanced README.md

• Provide a clearer overview of the project’s goal — is it for beginners, interview prep, competitive programming, etc.?
• Briefly explain the folder structure (e.g., /Array, /Linked List, /Sorting) and what kind of problems are inside each.
• Add a sample compilation and run command for C++ files (e.g., g++ main.cpp -o main && ./main) so beginners can test easily.
• Include an input/output example for at least one file so users know how to use/test the code.

2. Contribution Guidelines (CONTRIBUTING.md)

• Explain how to contribute: How to create a new folder or add to an existing one, how to name files (e.g., reverse_array.cpp instead of RA.cpp) and recommended code style: indentation, naming conventions, use of comments, etc.
• Mention prerequisites: preferred compiler version (e.g., C++11/C++17), tools (e.g., Code::Blocks, VS Code, CLion), and how to set up the environment.
• Instructions for adding test cases (if any), or how contributors can add basic input/output to verify functionality.

3. Add GitHub Templates

• Issue Template: So users know what to include when reporting a bug or requesting a new feature (e.g., code snippet, expected vs. actual output, environment info).
• Pull Request Template: Checklist: Does the code compile? Are there at least one or two sample inputs? Is the file named properly? Is the folder structured correctly?

Why This Helps

Improving documentation will:

• Make the repo more welcoming to new contributors
• Reduce confusion on how to add or test code
• Maintain consistency in folder and file structure
• Save maintainer time by encouraging clean, review-ready PRs

Let me know if you'd like help drafting the actual files (README.md, CONTRIBUTING.md, or templates). Happy to contribute!