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)
• [x] 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
• [x] Machine Learning
• [x] Open Source
• [ ] Python
• [ ] Rust
• [ ] Statistics
• [ ] UI/UX

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Checklist ✅

• [x] I follow Contributing Guidelines & Code of conduct of this project.
• [x] I have performed a self-review of my own code or work.
• [x] I have commented my code, particularly in hard-to-understand areas.
• [x] 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?