bpo-22295: use python -m pip rather than plain pip in more examples (GH-24003)

Doc/library/importlib.metadata.rst

@@ -43,7 +43,7 @@ something into it:
 
     $ python3 -m venv example
     $ source example/bin/activate
-    (example) $ pip install wheel
+    (example) $ python -m pip install wheel
 
 You can get the version string for ``wheel`` by running the following:
 

Doc/library/itertools.rst

@@ -721,7 +721,7 @@ Substantially all of these recipes and many, many others can be installed from
 the `more-itertools project <https://pypi.org/project/more-itertools/>`_ found
 on the Python Package Index::
 
-    pip install more-itertools
+    python -m pip install more-itertools
 
 The extended tools offer the same high performance as the underlying toolset.
 The superior memory performance is kept by processing elements one at a time