Added Stack and IntroductionToStack.md file

[IRFANSARI]

📥 Pull Request

Description

I have added a Stack folder in docs folder. In the stack folder, I have added a IntroductionToStack.md file that talks about stack introduction and implementation.

Fixes # (issue number)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[ajay-dhangar]

Thank you for your contributions. 👍 I appreciate your work on this. It's great!