Add `CLAUDE.md` and update `README.md` #595

Job	Run time
Check for Unneeded Dependencies	34s
Build and Cache Polkadot Binaries on ubuntu-24.04	10s
Check Clippy Lints	3m 7s
Check Formatting	33s
Build and Cache Polkadot Binaries on macos-14	9s
Unit Tests (ubuntu-24.04)	3m 39s
Unit Tests (macos-14)	4m 39s
	12m 51s

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