Added GitHub CheatSheet, ML Roadmap and OOPS Concept

[SrishtiSinha2003]

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Description 📜

Fixes # <8963>

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Type of change 📝

• Audio (Should be in mp3 format Includes speech clarity, Concise ,Low distortion)
• Video (Animations, screen-recordings, presentations and regular explanatory films are all possibilties etc)
• Documentation (Content Creation in the form of codes or tutorials)
• Other (If you choose other, Please mention changes below)

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Domain of Contribution 📊

• Android Dev (Flutter, Java, Kotlin)
• Backend Dev (Java, .NET, Python)
• C/CPP
• Competitive Programming
• Cyber Security
• DSA
• Database
• Datascience with Python
• Datascience with R
• Frontend Dev (HTML, CSS, JS)
• Frontend Dev (React, Angular, Vue)
• Golang
• Interview Prep
• Java
• JavaScript
• MERN
• Machine Learning
• Open Source
• Python
• Rust
• Statistics
• UI/UX

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Checklist ✅

• I follow Contributing Guidelines & Code of conduct of this project.
• I have performed a self-review of my own code or work.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generates no new warnings.
• I'm GWOC'21 contributor

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Screenshots / Gif (Optional) 📸

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[SrishtiSinha2003]

Hi! Just checking in — is there anything you'd like me to update or improve in this PR?