[Documentation]: Typos in Model_notation.md

[cfe316]

Bug description

In model_notation.md:

• \mathcal{X} ($\mathcal{X}$) is used for unit commitment startup decisions instead of \chi ($\chi$).
• v ($v$) is used for unit commitment state instead of \nu ($\nu$).

This would make the notation consistent with that in thermal_commit.jl and other places.

Environment and Version

n/a

Relevant error messages

No response

Additional context

No response

[lbonaldo]

Thanks @cfe316 for fixing these typos. I'm closing this issue as resolved.