Added references vs pointers under day 11

[muskan42]

Fix #210
List of the contents for "References vs Pointers in C++":

1. What are References and Pointers in C++?
2. Declaring References and Pointers
   • Declaring References
   • Declaring Pointers
3. Differences Between References and Pointers
   • Syntax and Usage
   • Initialization
   • Reassignment
   • Null Values
   • Memory Address
4. When to Use References and Pointers
   • Use References
   • Use Pointers
5. Examples
   • Example 1: Using References
   • Example 2: Using Pointers
6. Conclusion

@subhadipbhowmik kindly review

[github-actions]

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