Add info about fonts and figures

[bollu]

Add info about default font, and how to think about paper sizes when making figures.

[tobiasgrosser]

@bollu, any update on this.

@Superty, you might want to check this out with respect to the overly large figure in your paper.

[bollu]

@tobiasgrosser I am unsure about how accurate the above advice is about matplotlib. I have had success with it, but I don't understand all the interactions here. For example, where is the dpi and figsize information stored, when we produce a .pdf with matplotlib? Which part of TeX is responsible for interpreting these when we use \includegraphics{}?

I suggest we merge this PR if we are confident that the above is useful, and then iterate on the accuracy of the information about PDF sizing.

[tobiasgrosser]

@math-fehr @bollu, what's up with this? Should we move ahead with this or close this?

[bollu]

I’m happy to see it merged. I don’t particularly have the enthusiasm/cycles to figure out the answers to the questions above, to be honest, so I let you choose what to do with the PR.