Add chapter on describing config types

src/SUMMARY.md

@@ -17,4 +17,5 @@
   - [Communicating with humans](./in-depth/human-communication.md)
   - [Communicating with machines](./in-depth/machine-communication.md)
   - [Rendering documentation for your CLI apps](./in-depth/docs.md)
+  - [Rendering documentation for your Configuration](./in-depth/render-configuration.md)
 - [Resources](./resources/README.md)

src/in-depth/render-configuration.md

@@ -0,0 +1,46 @@
+# Rendering documentation for your Configuration
+
+If your application offers extensive configuration options, you may want to
+render these for the conveniance of the user.
+
+You could render them straight to the terminal, so that a user can "ask" your
+app what configuration it provides:
+
+```commandline
+myapp print-config-options
+```
+
+Using the [type_description crate](https://crates.io/crates/type_description)
+you can annotate your configuration struct(s) and let Rust do the magic:
+
+```rust,ignore
+use type_description::AsTypeDescription;
+use type_description::TypeDescription;
+use type_description::TypeKind;
+use type_description::Sign;
+
+/// A configuration
+#[derive(TypeDescription)]
+struct Config {
+    /// The bind address
+    addr: std::net::SocketAddr,
+
+    /// The Port
+    port: u16,
+}
+```
+
+The derive macro implements the `AsTypeDescription` on your `Config` type and
+uses the comments as descriptions.
+
+The `type_description` crate also implements the `AsTypeDescription` trait for
+the most common types for configuration from the standard library, such as
+numbers, `bool`, `String`, but also `Option`, `Vec` or `HashMap`.
+
+You can then use `Config::as_type_description()` to get the description for your
+`Config` type.
+
+You can render this information to a web-page, pdf, or simply to text and
+print it on the commandline (render functionality
+[within the type_description crate is currently unreleased](https://github.com/TheNeikos/type_description/blob/master/src/render.rs#L70)).
+