Revise Siren documentation #19410

Job	Run time
Check for 'skip-ci' label	1s
check-code	13m 31s
check-msrv	5m 25s
lockbud	14m 3s
target-branch-check	1s
op-pool-tests	15m 40s
release-tests-windows	34m 44s
debug-tests-ubuntu	8m 47s
beacon-chain-tests	20m 14s
network-tests	19m 4s
release-tests-ubuntu	28m 57s
slasher-tests	1m 46s
state-transition-vectors-ubuntu	2m 15s
basic-simulator-ubuntu	13m 47s
cargo-udeps	7m 41s
cli-check	7m 12s
compile-with-beta-compiler	15m 2s
ef-tests-ubuntu	13m 49s
execution-engine-integration-ubuntu	10m 34s
fallback-simulator-ubuntu	11m 33s
test-suite-success	4s
	4h 4m 10s

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