Reorder and tweak README.md sections

[kevinhartman]

Changes:

• Moves project history toward the bottom of the page to make it clearer that Rustworkx is freestanding and has utility beyond just Qiskit.
• Moves usage upwards, since this is often how new potential users will evaluate how well the library will suit their needs.
• Move project description upward so it's easier to see, and make it a bit more concise.

[coveralls]

Pull Request Test Coverage Report for Build 8073664787

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 96.517%

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Totals
Change from base Build 8023038916:	0.0%
Covered Lines:	16821
Relevant Lines:	17428

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💛 - Coveralls