[cmake][python][doc] Document all parameters of dune_add_python_test

cmake/modules/DunePythonTestCommand.cmake

@@ -16,6 +16,16 @@
 #       The Python module to execute using the python interpreter. It will be executed during :code:`make test_python`
 #       and during `ctest`. You are required to either pass SCRIPT or MODULE.
 #
+#    .. cmake_param:: LABELS
+#       :multi:
+#
+#       A list of labels to add to the test. This sets
+#       the LABELS property on the test so :code:`ctest -L ${label_regex}` can
+#       be used to run all tests with certain labels. We always add the label
+#       :code:`python` per default. The labels are forwarded to
+#       :ref:`dune_add_test`. See :ref:`dune_add_test` for a
+#       more detailed documentation.
+#
 #    .. cmake_param:: WORKING_DIRECTORY
 #       :single:
 #       :argname: dir
@@ -23,6 +33,13 @@
 #       The working directory of the command. Defaults to
 #       the current build directory.
 #
+#    .. cmake_param:: TIMEOUT
+#       :single:
+#
+#       If set, the test will time out after the given number of seconds. This supersedes
+#       any timeout setting in ctest (see `cmake --help-property TIMEOUT`). If you
+#       specify the MPI_RANKS option, you need to specify a TIMEOUT.
+#
 #    .. cmake_param:: NAME
 #       :single:
 #