Add markdown example

Author: gabotechs

examples/localhost.md

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+# Localhost workers example
+
+This example executes a SQL query in a distributed context.
+
+For this example to work, it's necessary to spawn some localhost workers with the `localhost_worker.rs` example:
+
+## Preparation
+
+This example queries a couple of test parquet we have for integration tests, and those files are stored using `git lfs`,
+so pulling the first is necessary.
+
+```shell
+git lfs checkout
+```
+
+### Spawning the workers
+
+In two different terminals spawn two ArrowFlightEndpoints
+
+```shell
+cargo run --example localhost_worker -- 8080 --cluster-ports 8080,8081
+```
+
+```shell
+cargo run --example localhost_worker -- 8081 --cluster-ports 8080,8081
+```
+
+- The positional numeric argument is the port in which each Arrow Flight endpoint will listen
+- The `--cluster-ports` parameter tells the Arrow Flight endpoint all the available localhost workers in the cluster
+
+### Issuing a distributed SQL query
+
+Now, DataFusion queries can be issued using these workers as part of the cluster.
+
+```shell
+cargo run --example localhost_run -- 'SELECT count(*), "MinTemp" FROM weather GROUP BY "MinTemp"' --cluster-ports 8080,8081
+```
+
+The head stage will be executed locally in the same process as that `cargo run` command, but further stages will be
+delegated to the workers running on ports 8080 and 8081.
+
+Additionally, the `--explain` flag can be passed to render the distributed plan:
+
+```shell
+cargo run --example localhost_run -- 'SELECT count(*), "MinTemp" FROM weather GROUP BY "MinTemp"' --cluster-ports 8080,8081 --explain
+```
+
+### Available tables
+
+Two tables are available in this example:
+
+- `flights_1m`: Flight data with 1m rows
+- `weather`: Small dataset of weather data