Add documentation for stack

[ashmeet-ashmeet]

Description

I'll be updating the current empty stack readme. It'll comprise of:

• Introduction
• Implementation (using both array and linked list)
• Basic operations

Programming language

• [ ] C
• [x] C++
• [ ] Java
• [ ] Python

Are you contributing under any open-source program ?

HSOC22

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[Chaitalishetty]

@ashmeet-chhabra Assigning you this issue. Happy coding!