Added GitHub Desktop contribution instructions

[PradnyaGaitonde]

Fixes Issue🛠️

Closes #733

Description👨‍💻

Successfully added instructions to contribute using GitHub Desktop in CONTRIBUTING_GUIDELINES.md file.

Type of change📄

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How this has been tested✅

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 @PradnyaGaitonde, 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 🥳 @PradnyaGaitonde