Update docs.

Author: dereuromark

README.md

@@ -3,8 +3,19 @@
 [![CI](https://github.com/cakephp/upgrade/actions/workflows/ci.yml/badge.svg)](https://github.com/cakephp/upgrade/actions/workflows/ci.yml)
 
 Upgrade tools for CakePHP meant to facilitate migrating between CakePHP 4.x
-versions and from CakePHP 4.x to CakePHP 5.x. This repository should be used as a standalone
-application and *not* as a plugin.
+versions, from CakePHP 4.x to CakePHP 5.x, and between CakePHP 5.x versions.
+This repository should be used as a standalone application and *not* as a plugin.
+
+## Table of Contents
+
+- [Installation](#installation)
+- [Usage](#usage)
+- [Upgrading between CakePHP 4.x versions](#upgrading-between-cakephp-4x-versions)
+- [Upgrading from CakePHP 4.x to CakePHP 5.0](#upgrading-from-cakephp-4x-to-cakephp-50)
+- [Upgrading between CakePHP 5.x versions](#upgrading-between-cakephp-5x-versions)
+- [Additional Rulesets](#additional-rulesets)
+- [Upgrading from CakePHP 3.x to CakePHP 4.x](#upgrading-from-cakephp-3x-to-cakephp-4x)
+- [Development](#development)
 
 ## Installation
 
@@ -43,10 +54,66 @@ bin/cake upgrade rector --rules cakephp44 /path/to/your/app/src
 
 There are rules included for:
 
+- cakephp40
 - cakephp41
 - cakephp42
 - cakephp43
 - cakephp44
+- cakephp45
+
+## Upgrading from CakePHP 4.x to CakePHP 5.0
+
+When upgrading from CakePHP 4.x to CakePHP 5.0, use the `cakephp50` ruleset to
+automate many of the required changes:
+
+```bash
+cd /path/to/upgrade
+
+# Apply upgrade rules from 4.x to 5.0
+bin/cake upgrade rector --rules cakephp50 /path/to/your/app/src
+bin/cake upgrade rector --rules cakephp50 /path/to/your/app/tests
+bin/cake upgrade rector --rules cakephp50 /path/to/your/app/config
+```
+
+## Upgrading between CakePHP 5.x versions
+
+When upgrading between CakePHP 5.x versions, use the appropriate ruleset for
+the target version:
+
+```bash
+cd /path/to/upgrade
+
+# To apply upgrade rules from 5.2 to 5.3
+bin/cake upgrade rector --rules cakephp53 /path/to/your/app/src
+```
+
+There are rules included for:
+
+- cakephp50
+- cakephp51
+- cakephp52
+- cakephp53
+
+## Additional Rulesets
+
+The upgrade tool also includes rulesets for related tools and libraries:
+
+- **chronos3** - Upgrade to Chronos 3.x
+- **migrations45** - Upgrade to Migrations 4.5
+- **phpunit80** - Upgrade to PHPUnit 8.0
+
+```bash
+cd /path/to/upgrade
+
+# Apply Chronos 3 upgrade rules
+bin/cake upgrade rector --rules chronos3 /path/to/your/app/src
+
+# Apply Migrations 4.5 upgrade rules
+bin/cake upgrade rector --rules migrations45 /path/to/your/app/config
+
+# Apply PHPUnit 8.0 upgrade rules
+bin/cake upgrade rector --rules phpunit80 /path/to/your/app/tests
+```
 
 ## Upgrading from CakePHP 3.x to CakePHP 4.x