docs: improve setup instructions and add missing matplotlib dependency (fix #29)

[Himesh021]

Changes

• Improved virtual environment setup instructions for Windows, Linux, and macOS
• Added Git Bash activation instructions for Windows users
• Clarified PowerShell execution policy step
• Documented handling of missing dependencies
• Added matplotlib dependency to requirements.txt

Problem

The setup instructions were incomplete and the project failed to run after following README steps due to missing dependency (matplotlib).

Testing

• Tested setup on Windows using Git Bash and PowerShell
• Verified virtual environment activation
• Verified dependency installation
• Confirmed Flask app runs successfully after changes

Fixes #29

[mahek-builds]

I would like to contribute to this project by fixing all the issues.

[mahek-builds]

Hi @Himesh021 and @maintainers,

I tested the project setup locally and confirmed that the application fails due to a missing matplotlib dependency in the current main branch.

After installing matplotlib manually, the application runs successfully.
I have fixed this issue in my fork — please review my changes and merge the pull request.

Thanks!