Add release notes for PR #5781: bevy_reflect: Recursive registration (#1282)

Co-authored-by: Alice Cecile <[email protected]>
Co-authored-by: Pascal Hertleif <[email protected]>

Author: 3 people

release-content/0.14/release-notes/5781_bevy_reflect_Recursive_registration.md

@@ -1 +1,39 @@
-TODO
+Bevy uses [reflection](https://docs.rs/bevy_reflect/latest/bevy_reflect/) in order to dynamically process data for things like serialization and deserialization.
+A Bevy app has a `TypeRegistry` to keep track of which types exist.
+Users can register their custom types when initializing the app or plugin.
+
+```rust
+#[derive(Reflect)]
+struct Data<T> {
+  value: T,
+}
+
+#[derive(Reflect)]
+struct Blob {
+  contents: Vec<u8>,
+}
+
+app
+  .register_type::<Data<Blob>>()
+  .register_type::<Blob>()
+  .register_type::<Vec<u8>>()
+```
+
+In the code above, `Data<Blob>` depends on `Blob` which depends on `Vec<u8>`,
+which means that all three types need to be manually registered—
+even if we only care about `Data<Blob>`.
+
+This is both tedious and error-prone, especially when these type dependencies are only
+used in the context of other types (i.e. they aren't used as standalone types).
+
+In 0.14, any type that derives `Reflect` will automatically register all of its type dependencies.
+So when we register `Data<Blob>`, `Blob` will be registered as well (which will register `Vec<u8>`),
+thus simplifying our registration down to a single line:
+
+```rust
+app.register_type::<Data<Blob>>()
+```
+
+Note that removing the registration for `Data<Blob>` now also means that `Blob` and `Vec<u8>` may 
+not be registered either, unless they were registered some other way. 
+If those types are needed as standalone types, they should be registered separately.