Bodies.trapezoid slope documentation not detailed enough

[ZufengW]

I was trying to use Bodies.trapezoid, but got confused because my trapezoids looked strange. Turns out this was because I was using slope values >= 1. I only figured out I should be using values < 1 by reading #138 (comment)

This expected value range should be added to the documentation. Maybe also add a warning if the user provides invalid trapezoid dimensions.

Doc link: https://brm.io/matter-js/docs/classes/Bodies.html#method_trapezoid

Some examples could also help. The "Examples" link in the doc currently shows no results.