Convert sipnet_inputs_outputs.doc to md

[dlebauer]

Hopefully for easier reference.

Exported sipnet_inputs_outputs.doc from google docs to md, then cleaned up formatting and added TOC

[Alomir]

I think a lot of the latex-style formatting is not working, due to misplaced $s? (That is, most everything in the rightmost column)

[Alomir]

At least, I can't get it to look right in github (or vscode) - but I do notice that the equivalent formatting in this PR worked fine when exported to PDF.

[dlebauer]

@Alomir it looks like a bug in GitHub's math processing. In the end I realized the latex formatting wasn't necessary at this point because 1) it was only being used for degrees, times, and superscripts and 2) these equations will eventually move to Doxygen.

FWIW, Github markddown does support math https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/writing-mathematical-expressions. But it has some bugs / limitations, apparently including that it doesn't like using $^ for superscripts which on reflection is probably a misuse of the feature.