docs: specify how asyncio's mode can be set

Author: JP-Ellis

docs/source/concepts.rst

@@ -16,7 +16,12 @@ You can think of `event_loop` as an autouse fixture for async tests.
 Test discovery modes
 ====================
 
-Pytest-asyncio provides two modes for test discovery, *strict* and *auto*.
+Pytest-asyncio provides two modes for test discovery, *strict* and *auto*. This can be set through Pytest's ``--asyncio-mode`` command line flag, or through the configuration file:
+
+.. code-block:: toml
+
+    [tool.pytest.ini_options]
+    asyncio_mode = "auto" # or "strict"
 
 
 Strict mode