Partly unreadable pdf documentation

[w_m0zartUBports]

@mariogrip FYI: In the documentation at:

https://docs.ubports.com/_/downloads/pt/latest/pdf/

there are many excerpts from the terminal which has white text on white background, like:

This makes it hard to read. Can this be improved?

[arubislander]

@w_m0zartubports please don't ping mariogrip directly, even if it is his name on the documentation referenced.