Slightly reword the docs about default main behavior

Explicitly mention reading arguments from `sys.argv` to avoid any confusion.

Co-authored-by: Ran Benita <ran@unusedvar.com>

doc/en/how-to/usage.rst

@@ -173,8 +173,7 @@ You can invoke ``pytest`` from Python code directly:
 
 this acts as if you would call "pytest" from the command line.
 It will not raise :class:`SystemExit` but return the :ref:`exit code <exit-codes>` instead.
-Be careful though, by default (when ``None`` is passed) ``main`` will read arguments
-from the command line, which may not be desirable.
+If you don't pass it any arguments, ``main`` reads the arguments from the command line arguments of the process (:data:`sys.argv`), which may be undesirable.
 You can pass in options and arguments explicitly:
 
 .. code-block:: python

src/_pytest/config/__init__.py

@@ -139,7 +139,7 @@ def main(
 
     :param args:
         List of command line arguments. If `None` or not given, defaults to reading
-        arguments directly from the command line.
+        arguments directly from the process command line (:data:`sys.argv`).
     :param plugins: List of plugin objects to be auto-registered during initialization.
 
     :returns: An exit code.