docs(changelog)!: Remove support for array-style mappings

In a previous commit (SHA: `76040df`), I forgot to mark it as a breaking
change. Thus, this commit also serves to mark that breaking change for
versioning purposes.

CHANGELOG.md

@@ -8,11 +8,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+This release contains **BREAKING CHANGES**. See the [v5.0 Upgrade Guide][breaking5] for required
+changes you may need to make.
+
+[breaking5]: https://recyclarr.dev/wiki/upgrade-guide/v5.0
+
 ### Changed
 
 - API Key is now sent via the `X-Api-Key` header instead of the `apikey` query parameter. This
   lessens the need to redact information in the console.
 
+### Removed
+
+- **BREAKING**: Array-style instances are no longer supported.
+
 ## [4.4.1] - 2023-04-08
 
 ### Fixed