Doc: faq: add differences from std raft #2852

Job	Run time
Build (nightly, bench,serde,bt,singlethreaded)	47s
openraft-test (stable, 0)	2m 58s
openraft-test (nightly, 30)	3m 18s
openraft-test (nightly, 0, single-term-leader)	2m 58s
cluster-benchmark (cluster_benchmark)	44s
external-stores (stores/rocksstore-v2)	5m 50s
examples (stable, raft-kv-memstore)	2m 17s
lint	6m 28s
examples (stable, raft-kv-rocksdb)	7m 56s
examples (nightly, raft-kv-memstore)	2m 14s
openraft-feature-test (nightly)	49s
openraft-feature-test (nightly, serde)	49s
examples (nightly, raft-kv-rocksdb)	11m 51s
openraft-feature-test (nightly, single-term-leader)	46s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	48s
openraft-test-bench (nightly)	1m 4s
stores (memstore)	42s
stores (rocksstore)	5m 56s
tests-feature-test (nightly)	2m 39s
stores (rocksstore-compat07)	6m 2s
tests-feature-test (nightly, single-term-leader)	2m 41s
tests-feature-test (nightly, loosen-follower-log-revert)	2m 42s
stores (sledstore)	54s
	1h 13m 13s

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