Doc: add License link #2720

Job	Run time
Build (nightly, bench,serde,bt,singlethreaded)	46s
external-stores (stores/rocksstore-v2)	5m 47s
cluster-benchmark (cluster_benchmark)	1m 8s
openraft-feature-test (nightly)	49s
openraft-feature-test (nightly, serde)	1m 16s
openraft-test (stable, 0)	2m 57s
openraft-feature-test (nightly, single-term-leader)	47s
openraft-test (nightly, 30)	4m 45s
openraft-test-bench (nightly)	1m 28s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	1m 30s
openraft-test (nightly, 0, single-term-leader)	3m 0s
stores (memstore)	1m 2s
stores (rocksstore)	13m 48s
tests-feature-test (nightly)	2m 40s
stores (rocksstore-compat07)	12m 12s
tests-feature-test (nightly, single-term-leader)	2m 42s
stores (sledstore)	1m 44s
tests-feature-test (nightly, loosen-follower-log-revert)	3m 47s
examples (stable, raft-kv-memstore)	2m 14s
examples (stable, raft-kv-rocksdb)	8m 2s
examples (nightly, raft-kv-memstore)	2m 8s
examples (nightly, raft-kv-rocksdb)	19m 14s
lint	11m 17s
	1h 45m 3s

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