docs: fix rendering of math equations

[Borda]

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What does this PR do?

some rendering was off

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[t-vi]

This is good. Thank you @Borda .

If and when we think it's too slow, we might think about https://pypi.org/project/sphinxcontrib-katex/ .

[t-vi]

Thank you @Borda @wujingyue

[Borda]

If and when we think it's too slow, we might think about pypi.org/project/sphinxcontrib-katex

did not know it, but yes we can check it if we ll face some more difficulties :)