Fix documentation math rendering issues

[TheodoreWolf]

Hello! I've started using Torax for a project of mine and found a few issues in the docs that I fixed :)

Describe the issue

There are a few documentation rendering issues specifically on the configuration page e.g.

The Fix

Just fixed the syntax so that MathJax renders properly. I took a few liberties to making the notation less heavy.

Result

Running make html yields:

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[Nush395]

Hi @TheodoreWolf, thanks a lot for the contribution and apologies for the very slow turnaround on review!

Would you mind syncing this change to HEAD and squashing the commit and we can bring it in when you have a chance, thanks!