Add update pip and setuptools section

CONTRIBUTING.rst

@@ -112,6 +112,22 @@ First time setup
              > py -3 -m venv env
              > env\Scripts\activate
 
+-   Update pip and setuptools.
+
+    .. tabs::
+
+       .. group-tab:: Linux/macOS
+
+          .. code-block:: text
+
+             $ python3 -m pip install --upgrade pip setuptools
+
+       .. group-tab:: Windows
+
+          .. code-block:: text
+
+             > py -3 -m pip install --upgrade pip setuptools
+
 -   Install the development dependencies, then install Flask in editable
     mode.