Update ReadMe.md

ReadMe.md

@@ -30,6 +30,7 @@ It allows to manage data providers with `zip()`, `join()`, `cross()`, `pairs()`,
 
 1. [Installation](#installation)
     * [Composer](#installation)
+2. [Migration](#mi)
 
 # Installation
 
@@ -38,3 +39,15 @@ Installation for PHP 7.1 and later:
 ```bash
 $ composer require --dev rawr/phpunit-data-provider
 ```
+
+# Migration from previous version
+
+To use version `3.0.0`, migrating from [`2.4.0`][previous] or earlier:
+
+- Library namespace changed from `\TRegx\DataProvider\ ` to `\TRegx\PhpUnit\DataProviders\ `.
+- Change `\TRegx\DataProvider\DataProviders::cross()` to `\TRegx\PhpUnit\DataProviders\DataProvider::cross()`.
+- Change `\TRegx\DataProvider\CrossDataProviders::cross()` to `\TRegx\PhpUnit\DataProviders\DataProvider::cross()`.
+- Change your data providers return type from `array` to `iterable` or `\TRegx\PhpUnit\DataProviders\DataProvider`.
+- Removed `\TRegx\DataProvider\CrossDataProviders::builder()`, use `\TRegx\PhpUnit\DataProviders\DataProvider::cross()` instead.
+
+[previous]: https://github.com/t-regx/CrossDataProviders/releases/tag/2.1.0