DOC: mention $$ instead of $

[mgeier]

The current text suggests that MathJax recognizes single $ by default, which is not true.

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[chrisjsewell]

Thnaks yeh I actually just remembered this whilst writing #378 lol

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Codecov Report

Merging #379 (cff92f4) into master (a39d236) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #379   +/-   ##
=======================================
  Coverage   90.54%   90.54%           
=======================================
  Files          14       14           
  Lines        1830     1830           
=======================================
  Hits         1657     1657           
  Misses        173      173           

Flag	Coverage Δ
pytests	90.54% <ø> (ø)

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[chrisjsewell]

As of #390, we now use the method of setting a top-level mathjax_ignore in myst documents and setting the MathJax config "processClass": "tex2jax_process|mathjax_process|math".
Therefore, this is no longer relevant.