docs/source/WritingTests.rst: update location of the whiteboard on test results

Signed-off-by: NCleber Rosa <crosa@redhat.com>

docs/source/WritingTests.rst

@@ -71,9 +71,8 @@ sleep length to be used by some other script or data analysis tool::
             time.sleep(self.params.sleep_length)
             self.whiteboard = "%.2f" % self.params.sleep_length
 
-The output path is always a file named ``whiteboard`` in the test result directory,
-the same directory where your ``debug.log`` file and ``sysinfo`` directory are located.
-
+The whiteboard can and should be exposed by files generated by the available test result
+plugins. The `results.json` file already includes the whiteboard for each test.
 
 Accessing test parameters
 =========================