Fix outdated pip install argument description

Author: xqm32

docs/html/cli/pip_install.rst

@@ -45,7 +45,7 @@ When looking at the items to be installed, pip checks what type of item
 each is, in the following order:
 
 1. Project or archive URL.
-2. Local directory (which must contain a ``setup.py``, or pip will report
+2. Local directory (which must contain a ``pyproject.toml`` or ``setup.py``, otherwise pip will report
    an error).
 3. Local file (a sdist or wheel format archive, following the naming
    conventions for those formats).