Add upgrade/migration doc

Author: DerManoMann

docs/.vitepress/config.js

@@ -20,6 +20,7 @@ function getGuideSidebar() {
     {
       text: 'Upgrading',
       children: [
+        { text: 'Migration from 4.x to 5.x', link: '/guide/migrating-to-v5' },
         { text: 'Migration from 3.x to 4.x', link: '/guide/migrating-to-v4' },
         { text: 'Migration from 2.x to 3.x', link: '/guide/migrating-to-v3' },
       ]

docs/guide/migrating-to-v5.md

@@ -0,0 +1,15 @@
+# Migrating to v5
+
+## Overview
+
+v5 is mostly a cleanup release with updated dependencies. The main changes are:
+
+* Minimum required PHP version is now 7.4
+* The legacy `TokenAnalyser` and the `--legacy` CLI option have been removed
+* Defaults now prefer attributes over annotations
+* PHP parsing now uses `nicic/php-parser`
+* Removal of deprecated features
+  * empty/unused `ProcessorInterface`
+  * `Context::clone()` and `Context::detect()`
+
+For most installations upgrading should not require any changes.