Merge branch 'lnd/v0.18.1-beta' and Update README #16

Job	Run time
RPC and mobile compilation check	5m 9s
Sqlc check	5m 5s
check commits	0s
lint code	55s
cross compilation	20s
check pinned dependencies (google.golang.org/grpc v1.59.0)	6s
sample configuration check	3m 50s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	5s
run unit tests (btcd unit-cover)	5m 21s
run macOS itest	5m 25s
run unit tests (unit tags="kvdb_etcd")	5m 20s
check release notes updated	4s
run unit tests (unit tags="kvdb_postgres")	5m 21s
run unit tests (unit tags="kvdb_sqlite")	5m 21s
run ubuntu itests (btcd, backend=btcd cover=1)	1m 26s
run windows itest	5m 15s
run unit tests (btcd unit-race)	5m 23s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	5m 22s
run unit tests (unit-module)	1m 25s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	5m 20s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	5m 8s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	5m 21s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	5m 19s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	5m 6s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	5m 9s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	4m 19s
run ubuntu itests (neutrino, backend=neutrino cover=1)	4m 14s
finish	4s
	1h 41m 13s

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