Add Unit Converter mini project

[Prajeeth-12]

Description

Unit Converter mini project

Checklist

• I've been assigned an issue related to this PR.
• [x ] I've used beautifiers.
• [ x] I've added my Project's name and description to Index.md
• [ x] I've made a README.md file for my Project.
• [ x] The README.md file of my projrct contains Project title, Description, Use of project, Set up, Stack used and Output

Related Issues or Pull Requests number

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