DOC: Fix setting make.bat options on Windows

figured this made more sense than opening a new PR for the docs

Author: story645

doc/devel/documenting_mpl.rst

@@ -82,12 +82,6 @@ it, use
 
    make SPHINXOPTS= html
 
-On Windows the arguments must be at the end of the statement:
-
-.. code-block:: bat
-
-   make html SPHINXOPTS=
-
 You can use the ``O`` variable to set additional options:
 
 * ``make O=-j4 html`` runs a parallel build with 4 processes.
@@ -97,12 +91,11 @@ You can use the ``O`` variable to set additional options:
 Multiple options can be combined using e.g. ``make O='-j4 -Dplot_gallery=0'
 html``.
 
-On Windows, either put the arguments at the end of the statement or set the options as environment variables, e.g.:
+On Windows, set the options as environment variables, e.g.:
 
 .. code-block:: bat
 
-   set O=-W --keep-going -j4
-   make html
+   set SPHINXOPTS= & set O=-j4 -Dplot_gallery=0 & make html
 
 Showing locally built docs
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