LaTeX not rendering in MSliceTestGuide

[cailafinn]

Describe the bug
Angstroms symbols don't appear to be rendering properly here.

To Reproduce

1. Go here: https://developer.mantidproject.org/Testing/DirectInelastic/MSliceTestGuide.html

Expected behavior
Angstroms should be shown as the symbol rather than this red text

Screenshots

[AndreiSavici]

Depending on preferences, add

.. only:: html

  :math:`\renewcommand\AA{\overset{\circ}{A}}`

or

.. only:: html

  :math:`\renewcommand\AA{\mathring{A}}`

or

.. only:: html

  :math:`\renewcommand\AA{\text{Å}}`

at the beginning of the file

Based on spacetelescope/pysynphot#116