Improve documentation on memory requirements for testing
Improve documentation on memory requirements for testing

holdenk/spark-testing-base,mahmoudhanafy/spark-testing-base,snithish/spark-testing-base,mahmoudhanafy/spark-testing-base,mahmoudhanafy/spark-testing-base,holdenk/spark-testing-base,mahmoudhanafy/spark-testing-base,snithish/spark-testing-base,holdenk/spark-testing-base,snithish/spark-testing-base,snithish/spark-testing-base,holdenk/spark-testing-base