This commit uses the correct form of "it's".
"Its" is possessive describes a noun, while "it's" is a contraction that
is short for "it is". Since "ready" is not a noun, we must use the
contraction in this case.
In addition, this commit adds some missing commas.
Co-authored-by: Eliza Weisman <eliza@buoyant.io>
This adds a guide that explains how to implement a middleware from scratch without taking any shortcuts. It walks through implementing `Timeout` as it exists in Tower today.
The hope is that once users have read [the previous guide](https://tokio.rs/blog/2021-05-14-inventing-the-service-trait) followed by this one they should be fully equipped to implement their own middleware.
This adds the first Tower guide called "Inventing the `Service` trait". It attempts to motivate all the parts to `Service` by walking the user through how they could have invented `Service` themselves, from scratch. It goes into quite a bit of detail but hopefully it paints a somewhat complete picture in the end.
The next guide I want to write is about how to implement a proper `Timeout` middleware using `Layer`, pin-project, and all the bells and whistles.
Ref: https://github.com/tower-rs/tower/issues/33
