[docs] use a standard mono-width font for the docs

[bradzacher]

The website is setup to use IosevkaCurly as the default font for code.
I personally found this font was very hard to read -- its characters are significantly thinner than a standard monospaced font.

IosevkaCurly

Menlo (the first fallback font)

I understand that some might have a stylistic preference here -- but it really strains my eyes trying to read the thinner font.

[bradzacher]

Thank you so much for actioning this so fast!