Merge pull request #574 from FridaTveit/AddHintFileToRnaTranscription

hello-world: explain UnsupportedOperationException in HINT.md file [Fix #350]

exercises/hello-world/HINT.md

@@ -0,0 +1,7 @@
+The default implementation for this exercise uses an [exception](https://docs.oracle.com/javase/tutorial/essential/exceptions/) 
+which will cause the test to fail with the provided error message.
+This particular exception type, [UnsupportedOperationException](http://docs.oracle.com/javase/8/docs/api/?java/lang/UnsupportedOperationException.html), 
+is commonly thrown to alert developers that a method has not yet been implemented.
+Throwing exceptions in this manner means the tests will compile but not pass right away.
+
+To make the test pass you need to remove the line which throws the exception and replace it with your implementation of the method.