Add a bit of documentation for the test skips

docs/EXERCISE_README_INSERT.md

@@ -17,3 +17,6 @@ Execute the tests with:
 ```bash
 $ npm test
 ```
+
+As you work your way through the test suite, be sure to remove the `skip <|`
+calls from each test until you get them all passing!

exercises/hello-world/tests/Tests.elm

@@ -11,6 +11,10 @@ tests =
         [ test "Hello with no name" <|
             \() ->
                 Expect.equal "Hello, World!" (helloWorld Nothing)
+
+        -- Once you get the first test passing, remove the
+        -- `skip <|` (just leave the comma) on the next two
+        -- lines to continue!
         , skip <|
             test "Hello to a sample name" <|
                 \() ->