document this trick for spark

[scottdraves]

suggested by @jarutis

%%spark
val jars = Set(ClasspathManager.getJars().toArray: _*).mkString(",")
SparkSession.builder().config("spark.jars", jars)

[jpallas]

Hmm. It looks like toArray is being used as a shortcut to avoid importing JavaConverters. I can't decide if that's sleazy or clever. But can the classpath ever contain duplicates? The Set seems unnecessary.

[scottdraves]

good point joe, i simplified it.