Expanding guidelines for docs

## How can Bevy's documentation be improved?
I've been looking over the documentation a couple of times, thinking that a specific part is inconsistently or at least unusually written.

However, often times the content is still right and I'm not sure if this should or shouldn't be corrected.
I'm fully aware that to many rules would only scare people away therefore I suggest to only recommend them instead of strictly enforcing them.

Some example points out of my head:
* Should a link always point to the doc? [`Most links are pointed to the source code here`](https://docs.rs/bevy/latest/bevy/transform/components/struct.Transform.html)
* Should doc comments always end with a dot(.)?
* Are headlines always plural (e.g. \# Examples but only listing one example)

Also a weird thing that I noticed, is that [`the winit links here`](https://docs.rs/bevy/latest/bevy/winit/index.html) aren't working in the docs but do work in my editor