docs: change instructions for cloning the V repository to use `--dept… #334

Job	Run time
tests-sanitize-address-clang	2h 10m 31s
tests-sanitize-undefined-clang	1h 2m 27s
tests-sanitize-undefined-gcc	1h 40m 12s
tests-sanitize-address-gcc	2h 41m 33s
tests-sanitize-address-msvc	3m 53s
tests-sanitize-memory-clang	3h 26m 27s
	11h 5m 3s

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