Overhaul docs for Windows filemon install

sheesh, hopefully this is "most" of it..although definitely still not
all we need yet..

docs/base/install/windows/pip.rst

@@ -0,0 +1,36 @@
+
+=====
+ Pip
+=====
+
+If you have a "recent" version of Python installed then you should
+already have Pip installed as well.
+
+
+Sanity Check
+============
+
+Just to be sure you have it, open a new console (``cmd.exe``) and run
+a version check:
+
+.. code-block:: none
+
+   C:\>pip --version
+   pip 21.2.3 from C:\Program Files\Python39\lib\site-packages\pip (python 3.9)
+
+If that doesn't work then maybe try to close and re-open your console
+first.
+
+Note that the Pip version check is only expected to work if the Python
+version check *also* worked.  So maybe see also docs for that, in
+:ref:`python-sanity-check`.
+
+If the Python version check works but Pip still does not then maybe
+your Python version is too old?  In that case you probably need to
+install Pip.  The recommended method is via the ``get-pip.py`` script
+according to `these instructions`_.
+
+.. _these instructions: https://pip.pypa.io/en/latest/installing.html#install-pip
+
+If you're sure Pip is installed and yet the version check still fails,
+please file a bug report at https://redmine.rattailproject.org/