Link to ApplicationState's in-depth guide from the project structure …

…section.

docs/guide/dependency_injection/core_concepts/application_state.md

@@ -1,9 +1,8 @@
 # `ApplicationState`
 
 All the [`Singleton`][Lifecycle::Singleton] types that your application needs to access at runtime
-when processing a request are grouped together in a struct called [`ApplicationState`][ApplicationState].  
-The [`ApplicationState`][ApplicationState] is code-generated by Pavex:
-you don't have to write it yourself!
+when processing a request are grouped together in a struct called `ApplicationState`. 
+The `ApplicationState` is code-generated by Pavex: you don't have to write it yourself!
 
 It is defined in the [server SDK crate] and exported as a public type.  
 It is then used in the [server crate] as an input parameter

docs/guide/project_structure/index.md

@@ -114,22 +114,23 @@ It's right there in your filesystem: you can open it, you can read it, you can u
 to get a deeper understanding of how Pavex works under the hood.
 
 At the same time, you actually don't need to know how it works to use it.  
-As a Pavex user, **you only need to care about** the two public types it exports: **the `run` function and the `ApplicationState`
+As a Pavex user, **you only need to care about** the two public types it exports: **the `run` function and the [`ApplicationState`](#applicationstate)
 struct**.
 
 ### `ApplicationState`
 
-`ApplicationState` holds all the types with a [`Singleton` lifecycle][Lifecycle::Singleton]
-that your application needs to access at runtime when processing a request.
+[`ApplicationState`](../dependency_injection/core_concepts/application_state.md) holds all the types
+with a [`Singleton` lifecycle][Lifecycle::Singleton] that your application needs to access at runtime when processing a request.
 
-To build an instance of `ApplicationState`, the server SDK exposes a function called `build_application_state`.
+To build an instance of [`ApplicationState`](../dependency_injection/core_concepts/application_state.md), 
+the server SDK exposes a function called `build_application_state`.
 
 ### `run`
 
 `run` is the entrypoint of your application.  
 It takes as input:
 
-- an instance of `ApplicationState`
+- an instance of [`ApplicationState`](#applicationstate)
 - a [`pavex::server::Server`][Server] instance
 
 [`pavex::server::Server`][Server] holds the configuration for the HTTP server that will be used to serve your API:
@@ -157,7 +158,7 @@ That's why you need a **server crate**.
 ### The executable binary
 
 The server crate contains the `main` function that you'll be running to start your application.  
-In that `main` function you'll be building an instance of `ApplicationState` and passing it to `run`.
+In that `main` function you'll be building an instance of [`ApplicationState`](#applicationstate) and passing it to `run`.
 You'll be doing a few other things too: initializing your `tracing` subscriber, loading
 configuration, etc.
 
@@ -188,4 +189,4 @@ The `demo` project includes an example of such a test which you can use as a ref
 [middlewares]: ../middleware/index.md
 [error handlers]: ../errors/error_handlers.md
 [error observers]: ../errors/error_observers.md
-[cargo-px]: https://github.com/LukeMathWalker/cargo-px
+[cargo-px]: https://github.com/LukeMathWalker/cargo-px