Added an explanatory comment

Author: Dean Wampler

src/script/scala/progscala3/patternmatching/MatchChaining.scala

@@ -1,7 +1,7 @@
 // src/script/scala/progscala3/patternmatching/MatchChaining.scala
 
 for opt <- Seq(Some(1), None)
-yield opt match {
+yield opt match {  // Braces for clarity, but not required! Try removing them.
   case None => ""
   case Some(i) => i.toString
 } match {        // will match on the String from the previous match