Updated README with sbt options for running tests

Author: debasishg

README.md

@@ -25,6 +25,8 @@ libraryDependencies ++= Seq("com.lightbend" %%
 
 The library comes with an embedded Kafka server. To run the tests, simply run `sbt testOnly` and all tests will run on the local embedded server.
 
+> The embedded server is started and stopped for every test and takes quite a bit of resources. Hence it's recommended that you allocate more heap space to `sbt` when running the tests. e.g. `sbt -mem 1500`.
+
 ## Type Inference and Composition
 
 Here's a sample code fragment using the Scala wrapper library. Compare this with the Scala code from the same [example](https://github.com/confluentinc/kafka-streams-examples/blob/4.0.0-post/src/test/scala/io/confluent/examples/streams/StreamToTableJoinScalaIntegrationTest.scala) in Confluent's repository.