Remember to mention *where* docs can be improved

[bvssvni]

This is just a reminder that we still need to work on documentation to get crates ready for 1.0 releases. Documentation will be the most easily picked low hanging fruit the next five years. PRs are welcome!

In that regard, it is important that people remember mention where. I read several times of people banging their heads or climbing uphills when struggling with the docs, but they forgot to mention the specific crate. The Piston project is pretty huge so if you can give some pointers, then it's easier to look through the docs and come up with ideas to improve it.