Docs|Tutorials: Inconsistent reference style

[TimoEckstein]

Description of the issue
In the Cirq tutorials there is a variety of reference styles. Making these consistent would probably not only make a slightly better impression to the reader, but also would help them to identify references faster; in particularly if the references were placed consistently at the end of each file/page.

Examples of the current reference style variety:

• Journal style reference with Author, Title, Journal, DOI (Deutsch-Jozsa algorithm) https://quantumai.google/cirq/tutorials/educators/intro
• Link on author name https://quantumai.google/cirq/tutorials/educators/qaoa_ising
• Link on arXiv reference https://github.com/quantumlib/Cirq/blob/master/docs/tutorials/educators/chemistry.ipynb
• Link to journal article, without naming author, title or journal (Quantum teleportation) https://quantumai.google/cirq/tutorials/educators/textbook_algorithms

Suggestion to resolve the issue
Use journal-inspired consistent references and put them at the end of each file into a reference block, similar to:

• Numpy Docs: https://numpy.org/doc/stable/reference/generated/numpy.linalg.eigh.html
• Scipy Docs: https://docs.scipy.org/doc/scipy/reference/generated/scipy.sparse.linalg.eigsh.html
• Cirq Docs: https://quantumai.google/reference/python/cirq/ops/ISwapPowGate

Cirq version
cirq.master

xref #5151

[dabacon]

See #5220 for how we should format external links

[tanujkhattar]

Google Developer style guide: https://developers.google.com/style