[lldb][docs] Update instructions for debugging API tests

This adds the option to use the `breakpoint()` keyword as a way to debug
the API tests.

Author: chelcassanova

lldb/docs/resources/test.rst

@@ -602,8 +602,9 @@ will cause the script to print out the pid of the test and wait for a while
 until a debugger is attached. Then run ``lldb -p <pid>`` to attach.
 
 To instead debug a test's python source, edit the test and insert
-``import pdb; pdb.set_trace()`` at the point you want to start debugging. In
-addition to pdb's debugging facilities, lldb commands can be executed with the
+``import pdb; pdb.set_trace()`` or ``breakpoint()`` (Python 3 only) at the point you want to start debugging. The ``breakpoint()`` command can be used for any LLDB Python script, not just for API tests.
+
+In addition to pdb's debugging facilities, lldb commands can be executed with the
 help of a pdb alias. For example ``lldb bt`` and ``lldb v some_var``. Add this
 line to your ``~/.pdbrc``: