Doc: refine FAQ, add "What actions are required when a node restarts" #2706

Job	Run time
cluster-benchmark (cluster_benchmark)	49s
examples (stable, raft-kv-memstore)	2m 18s
external-stores (stores/rocksstore-v2)	12m 1s
examples (stable, raft-kv-rocksdb)	13m 18s
lint	13m 1s
openraft-feature-test (nightly)	48s
examples (nightly, raft-kv-memstore)	2m 4s
openraft-feature-test (nightly, serde)	1m 19s
openraft-test (stable, 0)	4m 4s
examples (nightly, raft-kv-rocksdb)	11m 46s
openraft-feature-test (nightly, single-term-leader)	1m 19s
openraft-test-bench (nightly)	1m 41s
openraft-test (nightly, 30)	3m 6s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	48s
openraft-test (nightly, 0, single-term-leader)	4m 19s
stores (memstore)	1m 0s
Build (nightly, bench,serde,bt,singlethreaded)	50s
tests-feature-test (nightly)	2m 38s
stores (rocksstore)	10m 49s
tests-feature-test (nightly, single-term-leader)	5m 6s
stores (rocksstore-compat07)	6m 8s
tests-feature-test (nightly, loosen-follower-log-revert)	4m 58s
stores (sledstore)	53s
	1h 45m 3s

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