Add example of generating a cert chain #510

Job	Run time
Measure coverage	8m 38s
build-windows	13m 0s
Clippy	41s
build (macOS-latest, stable)	9m 38s
build (ubuntu-latest, stable)	8m 56s
Documentation (stable)	58s
Format	15s
build (ubuntu-latest, beta)	1m 4s
Documentation (beta)	49s
build (ubuntu-latest, nightly)	9m 27s
Documentation (nightly)	57s
build (ubuntu-latest, stable 7 months ago)	11m 23s
Documentation (stable 7 months ago)	54s
	1h 6m 40s

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