Corrected the calculation in CGPA Percentage Calculator

[nehashekhawat255]

Fixes Issue🛠️

Closes #819

Description👨‍💻

I have corrected the formulas in CGPA Percentage Calculator and also updated the readme file for the same.

Type of change📄

• Bug fix (non-breaking change which fixes an issue)

How this has been tested✅

I have tested it by giving many inputs in the columns of CGPA and percentage both, and now it is functioning well.

Checklist✅

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added demonstration in the form of GIF/video file
• I am an Open Source Contributor

Screenshots/GIF📷

[github-actions]

Hey @nehashekhawat255, Welcome to the project CalcDiverse! 🎊
Thanks for your contribution! Your effort makes this project better. Keep it up! 🙌
Please wait for the PR to be reviewed. Happy Coding!! ✨

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[Rakesh9100]

Congrats on getting your PR merged to the repo under GSSOC 2k24 🎉 @nehashekhawat255