Merge pull request #159 from exercism/default-snippet

Add default introductory code example

docs/SNIPPET.txt

@@ -0,0 +1,10 @@
+module HelloWorld exposing (..)
+
+helloWorld : Maybe String -> String
+helloWorld name =
+    case name of
+        Just name ->
+            "Hello, " ++ name ++ "!"
+
+        Nothing ->
+            "Hello, World!"