change font for code samples

[spooky]

current font makes distinguishing one underscore and two underscores hard - came up during the queryset part where things like title__contains were typed in as title_contains

[olasitarska]

Our tutorial uses gitbook, we can't control fonts :(

[keikoro]

@spooky, do you think adding some sort of warning/"attention!" note would help?

[spooky]

I saw warning/attention notes in the tutorial, though that apparently wasn't enough for the students to avoid that mistake so although that would probably reduce the problem, I don't think it will eliminate it.