Manual Math Error Fix

[Sparks29032]

Fixing math error in the manual. Change requirements from matplotlib-base to matplotlib.

Using matplotlib-base breaks the command pip install -r https://raw.githubusercontent.com/diffpy/diffpy.pdfmorph/main/requirements/run.txt in our installation instructions in the README.rst.

[sbillinge]

Is there no way to make the matplotlib-base work? I would only like to require full matplotlib if we need full matplotlib (i.e., for plotting with a gui)

[Sparks29032]

There's no matplotlib-base for PyPi. On our conda recipe, we only use matplotlib-base in the feedstock.

Unless we change the pip install instructions pip install -r https://raw.githubusercontent.com/diffpy/diffpy.pdfmorph/main/requirements/run.txt, we need matplotlib in our run.txt.. Changing it in run.txt won't affect our conda build though, that will still use the bare bones one.

[sbillinge]

I reached to Tom Caswell for advice on this. We don't want to ship the full matplotlib if we can avoid it to reduce bloat. He may have a recommendation.

[sbillinge]

This seems to be failing tests. It is not installing then importing the stylesheet correctly. Please can you take a look.

Actually we need a way to delete the package bg_mpl_stylesheets, or better, have it resolve to bg-mpl-stylesheets, but either way, we kind of need pdfmorph to install and import correctly.

[Sparks29032]

@sbillinge Fixed in #132, this PR only changes the Manual (files changed are just the texinfo, and pdf).