Document command line arguments in readme

README.rst

@@ -41,3 +41,28 @@ while to complete. This can be a major headache when trying to
 run tests quickly. pytest-test-groups allows you to easily say
 "split my tests into groups of 10 tests and run the second group".
 This is primarily useful in the context of CI builds.
+
+
+Command-line Arguments
+----------------------
+
+.. option:: --test-group-count <N>
+
+   Total number of groups to split the tests into. There must be at least this many tests.
+
+.. option:: --test-group <I>
+
+   The ``[1, N]`` test group to run, where ``N`` is the ``--test-group-count`` argument.
+   Use ``0`` to run all tests.
+
+.. option:: --test-group-random-seed <SEED>
+
+   If provided, assigns tests to groups pseudo-randomly using the given seed.
+   The default is a consisten order based on test node id hash.
+
+.. option:: --test-group-by <method>
+
+   Method for assigning tests to groups. Valid options are:
+
+   - ``item`` (default): Split by individual test items (default behavior).
+   - ``filename``: Split by test files, all tests from a single file remain in the same group.