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docs: the readme halves, and says what each plugin actually adds #8

Job	Run time
checks (ship list, bundles, half-to-half parity)	11s
rust tests (the shell's 56 unit tests)	2m 14s
build win-x64	6m 32s
build linux-x64	5m 0s
build mac-arm64	4m 39s
build ${{ matrix.rid }} (extra)	0s
release	1s
	18m 37s