Added QM Part 1

[Lucaman99]

I added an introductory quantum mechanics section to the Qiskit Textbook! This is only Part 1 out of 2. Part 1 goes over quantum states, observables, the Schrödinger equation, and some examples. Part 2 will cover spin, the uncertainty principle, Heisenberg and Schrödinger pictures of QM, and hopefully a little bit of background on Adiabatic Theorem and the Variational Principle!

[CLAassistant]

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[frankharkins]

Thanks for your contribution. I'm closing this pull request as this repository is no longer used and is being archived. You can find the latest version of the Qiskit Textbook online at https://qiskit.org/learn/, and the new content repository at Qiskit/textbook. Please feel free to re-open this pull request there if it's still relevant.