Issue template doesn't render details tags properly

[lucianopaz]

Description

I just opened #152 using the bug report issue template. The problem is that the "reproducible code example" and "error message" text areas are rendered as python code. So the details tags are naturally completely ignored. I think that these text areas should be regular markdown, and start with a value, not a placeholder. The placeholder disappears immediately once you start typing, but the value will stay as part of the markdown. We could add the <details> tags there, with the relevant python markdown brackets in there.