docs(hermetic-build): improve usability of development guide (#12362) #627

Job	Run time
filter	1m 21s
build(25) except self-service clients	12m 31s
build (17)	13m 24s
build(8) except for gapic-generator-java	3m 52s
build(21) except self-service clients	12m 14s
build(8) for gapic-generator-java	10m 37s
build(8) for showcase	9m 31s
dependency_analyzer_unit_test	49s
build (11)	13m 53s
gapic-generator-java-bom	2m 21s
unmanaged_dependency_check	8m 8s
showcase (21)	10m 36s
showcase (25)	9m 35s
showcase (17)	10m 16s
showcase (11)	10m 32s
showcase-clirr	-1s
	2h 9m 39s

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