Doc: add license link #2717

Job	Run time
external-stores (stores/rocksstore-v2)	5m 54s
openraft-test-bench (nightly)	56s
openraft-test (stable, 0)	4m 26s
stores (memstore)	45s
openraft-test (nightly, 30)	3m 8s
Build (nightly, bench,serde,bt,singlethreaded)	48s
stores (rocksstore)	5m 50s
stores (rocksstore-compat07)	13m 32s
cluster-benchmark (cluster_benchmark)	45s
examples (stable, raft-kv-memstore)	3m 25s
stores (sledstore)	53s
openraft-test (nightly, 0, single-term-leader)	3m 12s
examples (stable, raft-kv-rocksdb)	6m 25s
lint	14m 29s
examples (nightly, raft-kv-memstore)	3m 18s
openraft-feature-test (nightly)	1m 9s
examples (nightly, raft-kv-rocksdb)	11m 45s
tests-feature-test (nightly)	2m 40s
openraft-feature-test (nightly, serde)	48s
tests-feature-test (nightly, single-term-leader)	2m 38s
openraft-feature-test (nightly, single-term-leader)	47s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	51s
tests-feature-test (nightly, loosen-follower-log-revert)	2m 40s
	1h 31m 4s

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