Document that using overrides disables all wheels

Update documentation to state that using command line options on any
requirements will disable all usage of wheels. Since this is unexpected
behavior, move text to a warning.

Author: martey

docs/html/cli/pip_install.rst

@@ -205,8 +205,11 @@ Per-requirement Overrides
 -------------------------
 
 Since version 7.0 pip supports controlling the command line options given to
-``setup.py`` via requirements files. This disables the use of wheels (cached or
-otherwise) for that package, as ``setup.py`` does not exist for wheels.
+``setup.py`` via requirements files.
+
+.. warning::
+
+   This disables the use of wheels (cached or otherwise).
 
 The ``--global-option`` and ``--install-option`` options are used to pass
 options to ``setup.py``. For example:

news/9674.doc.rst

@@ -0,0 +1 @@
+Clarify that using per-requirement overrides disables the usage of wheels.