Fix very trivial grammar issues & typos in docs/start/basics (#5752)
Fix very trivial grammar issues & typos in docs/start/basics (#5752)

This is such a trivial PR, but I spotted them and figured I may as well offer to fix them very quickly.

This fixes a couple of very tiny grammar bugs, plus a few cases of cirq -> Cirq capitalization, and some missing periods at the ends of list items (to make all lists on the page follow the same convention).
quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq