docs/linux: updated reporting security bugs guide #14360

Job	Run time
build	7m 33s
aux	4m 50s
dashboard	3m 11s
arch (presubmit_arch_linux)	10m 33s
gvisor	4m 10s
old	6m 23s
arch (presubmit_arch_freebsd)	6m 30s
race	7m 53s
arch (presubmit_arch_netbsd)	4m 18s
race_dashboard	5m 7s
arch (presubmit_arch_openbsd)	4m 12s
arch (presubmit_arch_darwin)	4m 20s
arch (presubmit_arch_windows)	3m 24s
arch (presubmit_arch_executor)	3m 19s
	1h 15m 43s

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