Try to use a different font for content

[ccordoba12]

According to the Pydata Sphinx theme docs, the theme use system fonts, which I don't like too much.

I'd like to use the same font we use in our website for consistency. But if you think that's not feasible, then we should use one from Google fonts, as we did for the Spyder 4 docs.

[conradolandia]

Solved by #411