Update intro and cbor quick start in README (#421)

Update README for v2.5.0
* Rewrite Quick Start
* Update intro to show Struct Tags and CBOR Security earlier.
* Removed sections: "Comparison", "Usage", "Why fxamacker/cbor", "CBOR Options", "API", etc.
* Removed files: CBOR_GOLANG.md, CBOR_BENCHMARKS.md, etc.
* Update CODE_OF_CONDUCT.md
* Add openssf scorecard badge but did not link to detailed report.
* Make Acknowledgements section placeholder because new contributors weren't included for years.