docs: Add docker compose setup with 3 node etcd cluster

[subkanthi]

closes: ##152
docker compose setup with 3 node etcd cluster.

 insert -p flowers.iris file://iris.parquet
2026-04-27 13:50:50 [-5-thread-1] INFO c.a.i.c.internal.cmd.Insert > file://iris.parquet: processing
2026-04-27 13:50:50 [-5-thread-1] INFO c.a.i.c.internal.cmd.Insert > file://iris.parquet: copying to s3://bucket1/flowers/iris/data/1777315850733-31e515659a185bbdc820b3b19c90384ca5a77530f265cdaa2313b8e0c6f9bd80.parquet
2026-04-27 13:50:51 [-5-thread-1] INFO c.a.i.c.internal.cmd.Insert > file://iris.parquet: adding data file (copy took 0s)
2026-04-27 13:50:51 [main] INFO o.a.i.SnapshotProducer > Committed snapshot 3873137362459299979 (MergeAppend)

[xieandrew]

Docker compose looks good overall, though I think we can update the etcd cluster setup docs
to mention this new file if someone wants a 3 node setup.

Also I noticed a couple issues with this ice command in the docs:

• The -p flag should be added to create a new table
• There's no mention of where the iris.parquet file is. It's not in examples/docker-compose so we should either copy it there or mention which directory it's in such as examples/scratch.

[xieandrew]

Maybe we should add commented ports map like the single node setup:

# Uncomment to run etcdctl from the host against this cluster:
# ports:
#   - "12379:2379"

Port numbers should match the etc-cluster-setup docs (12379, 12479, 12579)

[subkanthi]

updated