Update Federation.md

Federation.md

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 # Enabling Query Federation
 
+We use [accio](https://github.com/sfu-db/accio) to rewrite a federated query into multiple single-source ones, and combine the result locally with [datafusion](https://github.com/apache/datafusion).
+
+To enable query federation for connectorx:
+1. Clone accio: `[email protected]:sfu-db/accio.git`.
+2. Build accio: `cd accio/rewriter && mvn package -Dmaven.test.skip=true`.
+3. Move the jar file to location `${YOUR_LOCAL_PYTHON_PATH}/site-packages/connectorx/dependencies/federated-rewriter.jar`
+4. Configure accio and set the configuration path as `FED_CONFIG_PATH`. Example configurations can be found [here](https://github.com/sfu-db/accio/tree/main/benchmark/config/tpch10_datafusion/10gbit).
+5. Run federated query using connectorx!