Update the README

Author: poojanilangekar

extensions/federation/README.md

@@ -1,9 +1,13 @@
 ### Using the `HadoopFederatedCatalogFactory`
 
-This module is an independent compilation unit and will be built into the Polaris binary only when the following flag is set in gradle.properties or as a JVM arg at compile time:
-
+This `HadoopFederatedCatalogFactory` module is an independent compilation unit and will be built into the Polaris binary only when the following flag is set in the gradle.properties file:
 ```
 NonRESTCatalogs=HADOOP,<alternates>
 ```
 
+The other option is to pass it as an argument to the gradle JVM as follows: 
+```
+./gradlew build DNonRESTCatalogs=HADOOP
+```
+
 Without this flag, the Hadoop factory won't be compiled into Polaris and therefore Polaris will not load the class at runtime, throwing an unsupported exception for federated catalog calls.