Replace references to old book with quick start guide (bevyengine#11983)

# Objective

Since bevyengine/bevy-website#880, the old book
is now the Quick Start Guide, but the references to the old book have
not been updated.

## Solution

Update references to the old book to point to the Quick Start Guide.

README.md

@@ -13,7 +13,7 @@ Bevy is a refreshingly simple data-driven game engine built in Rust. It is free
 
 ## WARNING
 
-Bevy is still in the early stages of development. Important features are missing. Documentation is sparse. A new version of Bevy containing breaking changes to the API is released [approximately once every 3 months](https://bevyengine.org/news/bevy-0-6/#the-train-release-schedule). We provide [migration guides](https://bevyengine.org/learn/book/migration-guides/), but we can't guarantee migrations will always be easy. Use only if you are willing to work in this environment.
+Bevy is still in the early stages of development. Important features are missing. Documentation is sparse. A new version of Bevy containing breaking changes to the API is released [approximately once every 3 months](https://bevyengine.org/news/bevy-0-6/#the-train-release-schedule). We provide [migration guides](https://bevyengine.org/learn/migration-guides/), but we can't guarantee migrations will always be easy. Use only if you are willing to work in this environment.
 
 **MSRV:** Bevy relies heavily on improvements in the Rust language and compiler.
 As a result, the Minimum Supported Rust Version (MSRV) is generally close to "the latest stable release" of Rust.
@@ -34,7 +34,7 @@ As a result, the Minimum Supported Rust Version (MSRV) is generally close to "th
 
 ## Docs
 
-* **[The Bevy Book](https://bevyengine.org/learn/book/introduction):** Bevy's official documentation. The best place to start learning Bevy.
+* **[Quick Start Guide](https://bevyengine.org/learn/quick-start/introduction):** Bevy's official Quick Start Guide. The best place to start learning Bevy.
 * **[Bevy Rust API Docs](https://docs.rs/bevy):** Bevy's Rust API docs, which are automatically generated from the doc comments in this repo.
 * **[Official Examples](https://github.com/bevyengine/bevy/tree/latest/examples):** Bevy's dedicated, runnable examples, which are great for digging into specific concepts.
 * **[Community-Made Learning Resources](https://bevyengine.org/assets/#learning)**: More tutorials, documentation, and examples made by the Bevy community.
@@ -58,9 +58,9 @@ For more complex architecture decisions and experimental mad science, please ope
 
 ## Getting Started
 
-We recommend checking out [The Bevy Book](https://bevyengine.org/learn/book/introduction) for a full tutorial.
+We recommend checking out the [Quick Start Guide](https://bevyengine.org/learn/quick-start/introduction) for a brief introduction.
 
-Follow the [Setup guide](https://bevyengine.org/learn/book/getting-started/setup/) to ensure your development environment is set up correctly.
+Follow the [Setup guide](https://bevyengine.org/learn/quick-start/getting-started/setup) to ensure your development environment is set up correctly.
 Once set up, you can quickly try out the [examples](https://github.com/bevyengine/bevy/tree/latest/examples) by cloning this repo and running the following commands:
 
 ```sh
@@ -84,7 +84,7 @@ fn main(){
 
 ### Fast Compiles
 
-Bevy can be built just fine using default configuration on stable Rust. However for really fast iterative compiles, you should enable the "fast compiles" setup by [following the instructions here](http://bevyengine.org/learn/book/getting-started/setup/).
+Bevy can be built just fine using default configuration on stable Rust. However for really fast iterative compiles, you should enable the "fast compiles" setup by [following the instructions here](https://bevyengine.org/learn/quick-start/getting-started/setup).
 
 ## [Bevy Cargo Features][cargo_features]
 

src/lib.rs

@@ -6,7 +6,7 @@
 //! and performance.
 //!
 //! Check out the [Bevy website](https://bevyengine.org) for more information, read the
-//! [Bevy Book](https://bevyengine.org/learn/book/introduction) for a step-by-step guide, and [engage with our
+//! [Quick Start Guide](https://bevyengine.org/learn/quick-start/introduction) for a step-by-step introduction, and [engage with our
 //! community](https://bevyengine.org/community/) if you have any questions or ideas!
 //!
 //! ## Example