Update README with XCFramework deployment instructions

Author: mokagio

README.md

@@ -1,5 +1,23 @@
 #  WordPressKit for iOS
 
+<!-- red -->
+> [!CAUTION]
+> This library is no longer fit for external contribution and community usage.
+>
+> [WordPress iOS](https://github.com/wordpress-mobile/WordPress-iOS) is its only consumer.
+> The repo exists standalone rather than as part of the WordPress codebase because it's convenient to fetch this lump of code that rarely changes as a binary XCFramework dependency.
+> See [#816](https://github.com/wordpress-mobile/WordPressKit-iOS/pull/816).
+
+## XCFramework release instructions
+
+- Run `.buildkite/create-xcframeworks.sh` to create binaries
+- Upload `.build/xcframeworks/WordPressKit.zip` to this repo
+- Update binary target in `Package.swift` with a new URL and checksum<sup>*</sup>
+- Push the new changes to your branch
+- After testing is done, merge changes into `trunk`
+
+<sup>*</sup>_checksum is echoed at the end of the `create-xcframeworks.sh` script_
+
 ## About
 
 WordPressKit offers a clean and simple WordPress.com and WordPress.org API.