docs: add icon (#434) #1125

Job	Run time
format	12s
test	1m 40s
examples	26s
feature_set	4m 36s
msrv	19s
rust-clippy-analyze	54s
udeps	52s
engine_io (v3)	33s
socket_io (v4)	39s
engine_io (v4)	32s
socket_io (v5)	42s
socket_io (v5-msgpack)	44s
adapter (v4, fred-e2e)	1m 19s
adapter (v4, redis-e2e)	1m 9s
adapter (v4, redis-cluster-e2e)	1m 13s
adapter (v4, fred-cluster-e2e)	1m 12s
adapter (v4-msgpack, fred-e2e)	1m 54s
adapter (v4-msgpack, redis-e2e)	1m 9s
adapter (v4-msgpack, redis-cluster-e2e)	1m 19s
adapter (v4-msgpack, fred-cluster-e2e)	1m 9s
adapter (v5, fred-e2e)	1m 22s
adapter (v5, redis-e2e)	1m 18s
adapter (v5, redis-cluster-e2e)	1m 19s
adapter (v5, fred-cluster-e2e)	1m 20s
adapter (v5-msgpack, fred-e2e)	1m 41s
adapter (v5-msgpack, redis-e2e)	1m 37s
adapter (v5-msgpack, redis-cluster-e2e)	1m 15s
adapter (v5-msgpack, fred-cluster-e2e)	1m 23s
all_passed	1s
	33m 49s

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