add qft module

[kcmccormibm]

Adding Qiskit in Class module on QFT

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Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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[qiskit-bot]

Thanks for contributing to Qiskit documentation!

Before your PR can be merged, it will first need to pass continuous integration tests and be reviewed. Sometimes the review process can be slow, so please be patient. Thanks! 🙌

[kcmccormibm]

This module went through technical review with Abigail McClain-Gomez and is ready for copy-edit/upload