Simplify how to build Python SDK (apache#26693)

Co-authored-by: Ahmed Abualsaud <[email protected]>

website/www/site/content/en/documentation/io/built-in/google-bigquery.md

@@ -786,7 +786,8 @@ BigQuery Storage Write API for Python SDK currently has some limitations on supp
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-**Note:** If you want to run WriteToBigQuery with Storage Write API from the source code, you need to run `./gradlew :sdks:java:io:google-cloud-platform:expansion-service:build` to setup corresponding Java classes. If you want to run it from a released Beam SDK, you don't need to execute the command since the expansion service will be automatically downloaded and started.
+**Note:** If you want to run WriteToBigQuery with Storage Write API from the source code, you need to run `./gradlew :sdks:java:io:google-cloud-platform:expansion-service:build` to build the expansion-service jar. If you 
+are running from a released Beam SDK, the jar will already be included.
 
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