docs: add v5 beta announcement and upgrade guide

- Add announcement banner for v5.0.0 beta release
- Note v4.x maintenance mode status
- Add "From 4.x to 5.x" section to UPGRADE.md with breaking changes

Author: brettstack

README.md

@@ -1,4 +1,10 @@
 
+> **v5.0.0 Beta Released!** Version 5.0.0 is now available in beta with Node.js 24 support, removal of deprecated APIs, and a fix for nested routes and custom domains. Install with: `npm install @codegenie/serverless-express@beta`
+>
+> Upgrading should be seamless unless you relied on deprecated APIs. See [UPGRADE.md](UPGRADE.md#from-4x-to-5x) for details.
+>
+> **Note:** Version 4.x is now in maintenance mode and will only receive critical bug fixes.
+
 <h2 align="center">Serverless Express by</h1>
 <p align="center">
   <a href="https://codegenie.codes">

UPGRADE.md

@@ -1,3 +1,28 @@
+## From 4.x to 5.x
+
+Upgrading from v4.x to v5.x should be seamless for most users. If you were already using the recommended async/Promise pattern with `binarySettings`, no code changes are required.
+
+### Breaking Changes
+
+The following deprecated APIs have been removed:
+
+| Removed | Replacement |
+|---------|-------------|
+| `resolutionMode: 'CALLBACK'` | Use async/Promise (default) |
+| `resolutionMode: 'CONTEXT'` | Use async/Promise (default) |
+| `binaryMimeTypes` option | Use `binarySettings` instead |
+| `createServer()` export | Use `serverlessExpress({ app })` |
+| `proxy()` export | Use `serverlessExpress({ app })` |
+| `handler.handler()` | Use `serverlessExpress({ app })` |
+| `handler.proxy()` | Use `serverlessExpress({ app })` |
+| Callback parameter in handler | Use async/Promise |
+
+### Node.js Version
+
+v5.x officially supports Node.js 24+, aligning with AWS Lambda's latest runtime. Earlier Node.js versions may still work but are not officially supported.
+
+---
+
 ## From 3.x to 4.x
 
 ### Lambda Handler