Add missing section in classical shadows example #1558

Job	Run time
core	1m 44s
docs	50m 11s
validate	5m 33s
test-linux (ubuntu-latest, 3.8)	26m 15s
test-linux (ubuntu-latest, 3.9)	29m 33s
test-linux (ubuntu-latest, 3.10)	27m 54s
test-linux (ubuntu-latest, 3.11)	26m 42s
test-linux-draft	0s
test-nonlinux (macos-latest, 3.8)	31m 59s
test-nonlinux (macos-latest, 3.9)	29m 34s
test-nonlinux (macos-latest, 3.10)	30m 37s
test-nonlinux (macos-latest, 3.11)	27m 53s
test-nonlinux (windows-latest, 3.8)	40m 47s
test-nonlinux (windows-latest, 3.9)	27m 37s
test-nonlinux (windows-latest, 3.10)	33m 2s
test-nonlinux (windows-latest, 3.11)	29m 34s
test-nonlinux-draft	0s
	6h 58m 55s

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