Revise Siren documentation #18944

Job	Run time
check-code	9m 34s
Check for 'skip-ci' label	1s
check-msrv	5m 3s
lockbud	13m 34s
target-branch-check	1s
beacon-chain-tests	18m 17s
op-pool-tests	15m 37s
release-tests-ubuntu	18m 16s
debug-tests-ubuntu	10m 20s
release-tests-windows	17m 58s
slasher-tests	1m 39s
basic-simulator-ubuntu	13m 33s
cargo-udeps	7m 32s
cli-check	6m 46s
compile-with-beta-compiler	13m 19s
ef-tests-ubuntu	10m 27s
execution-engine-integration-ubuntu	10m 22s
fallback-simulator-ubuntu	11m 12s
network-tests	18m 14s
state-transition-vectors-ubuntu	2m 29s
test-suite-success	1s
	3h 24m 15s

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