src/doc/en/developer/doctesting.rst: Expand on --update-known-test-failures

Author: Matthias Koeppe

src/doc/en/developer/doctesting.rst

@@ -1693,7 +1693,10 @@ The modularized distribution packages ``pkgs/sagemath-categories`` and
 with the option ``--baseline-stats-path``, see section
 :ref:`section-doctest-auxiliary-files`.
 
-These files can be updated using the command::
+After running the doctesters of the distributions, for example, via
+``sage --fixdoctests``, you can use the test results stored in
+``timings2.json`` files to update the ``known-test-failures*.json`` files.
+This update can be done using the command::
 
     [mkoeppe@localhost sage]$ ./sage --fixdoctests --no-test                        \
                                 --update-known-test-failures --distribution all