Add upgrade document, add branch alias

Author: bobvandevijver

UPGRADE.md

@@ -0,0 +1,7 @@
+This file describes the steps you will need to make when upgrading this bundle.
+
+# From 1.x to 2.x
+
+The bundle drops support for PHP <8.1 and annotations, so you will need to update all your annotations to attributes!
+
+Other than that there are no changes.

composer.json

@@ -96,5 +96,10 @@
       "Drenso\\Shared\\": "src/",
       "Drenso\\Shared\\Tests\\": "phpunit/"
     }
+  },
+  "extra": {
+    "branch-alias": {
+      "dev-master": "v2.x-dev"
+    }
   }
 }