docs: add usage documentation under docs/ (#8) #16

Job	Run time
build / vet / test / lint	46s
resolve supported version window	4s
image build (k8s 1.36)	3m 19s
image build (k8s 1.35)	3m 23s
image build (k8s 1.34)	3m 32s
	11m 4s

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