Add upgrading notes

Author: AydinHassan

README.md

@@ -25,6 +25,7 @@
 
   * [Minimum Requirements](#minimum-requirements)
   * [Installation](#installation)
+  * [Upgrading](#upgrading)
   * [Usage](#usage)
     * [Quick Setup](#quick-setup)
     * [Examples](#examples)
@@ -75,6 +76,11 @@
 composer require php-school/cli-menu
 ```
 
+## Upgrading
+
+Please refer to the [Upgrade Documentation](UPGRADE.md) documentation to see what is required to upgrade your installed 
+`cli-menu` version.
+
 ## Usage
 
 ### Quick Setup

UPGRADE.md

@@ -0,0 +1,14 @@
+# Upgrade Documentation
+
+This document serves as a reference to upgrade your current cli-menu installation if improvements, deprecations
+or backwards compatibility (BC) breakages occur.
+
+## 3.0.0
+
+### BC breaks
+
+* Class `PhpSchool\CliMenu\CliMenuBuilder` has been moved, use 
+  `PhpSchool\CliMenu\Builder\CliMenuBuilder` instead. The old class has been aliased for now, but will be removed in 
+  `3.1`.
+* Removed `PhpSchool\CliMenu\Terminal` namespace, the code has been migrated to the `php-school/terminal` package and is 
+  largely modified.