Add debug.md (#490)

* Add debug.md

* Update exercises/shared/.docs/debug.md

* Update exercises/shared/.docs/debug.md

---------

Co-authored-by: Jeremy Walker <jez.walker@gmail.com>

exercises/shared/.docs/debug.md

@@ -0,0 +1,13 @@
+# Debug
+
+When a test fails, a message is displayed describing what went wrong and for which input.
+You can inspect arbitrary values in your program by passing them to the `debug` method (available at `exercism/test_runner`).
+This will capture the values and show you the output.
+
+
+```gleam
+import exercism/test_runner.{ debug }
+
+let value: String = "test"
+debug("The value is " <> value)
+```