[lldb][Docs] Link to testing page from debugging page

The testing page already has some page about debugging failures.

I'm not linking directly to that section because:
* The earlier sections about running single tests and such
  are just as useful for debugging in general.
* The new theme has a nice sidebar on the right that makes
  it really easy to find what you want once on the page.
* We'll probably add more content to the testing page later.

Author: DavidSpickett

lldb/docs/resources/debugging.rst

@@ -580,3 +580,8 @@ reproduction steps.
 Finally, that "thing" is the ptrace calls you got from the ``lldb-server`` logs.
 Add those to the debugger function and you now have a reproducer that doesn't
 need any part of LLDB.
+
+Debugging Tests
+---------------
+
+See :doc:`/resources/test`.