Create comprehensive Markdown documentation

[vampirepapi]

This commit introduces a new DOCUMENTATION.md file to serve as a comprehensive, beginner-friendly guide to the repository.

Key changes include:

1. Created DOCUMENTATION.md: A new central documentation file.
2. Quick Start Guide: Added a section to help you navigate the documentation and repository structure.
3. Design Patterns Documentation:
   • General introduction to design patterns.
   • Categorized into Creational, Structural, and Behavioral patterns.
   • Listed implemented patterns for each supported language (Javascript, C++, C#, Go, Java, Python) with links to code examples.
4. OOP Concepts Documentation:
   • Explanation of core OOP principles (Abstraction, Encapsulation, Inheritance, Polymorphism).
   • Listed implemented/explained OOP concepts for each language with links to relevant READMEs.
   • Included other related concepts like Classes/Objects, Interfaces, Association, Aggregation, and Composition.
5. Problems and Solutions Documentation:
   • Listed all available problem statements from the problems/ directory.
   • Provided links to solutions for each problem, organized by language, pointing to their respective READMEs in the solutions/ directory.
6. Learning Checklist/Roadmap: Added a suggested learning path through OOP concepts and design patterns, including estimated times and difficulty indicators.
7. General Information:
   • Added a "Contributing" section with guidelines for new contributions.
   • Added a "License" section referencing the existing GPLv3 license.
8. Updated README.md: Added a prominent link in the main README.md pointing to the new DOCUMENTATION.md file for improved discoverability.

This new documentation aims to make the repository more accessible and easier to learn from, especially for you if you are new to software design principles and patterns.