Update Doctrine.php: Adding upgrade instructions (#29)

src/Codeception/Module/Doctrine.php

@@ -38,10 +38,15 @@
 use function var_export;
 
 /**
+ * Upgrading from Module "Doctrine2":
+ * * In your `composer.json`: Replace `"codeception/module-doctrine2"` with `"codeception/module-doctrine"`
+ * * In your `Acceptance.suite.yml`, `Functional.suite.yml`, and `Unit.suite.yml`: Replace `- Doctrine2:` with `- Doctrine:`
+ * * In any file in `Support/Helper/`: Change `$this->getModule('Doctrine2')` to `$this->getModule('Doctrine')`
+ *
  * Access the database using [Doctrine ORM](https://docs.doctrine-project.org/projects/doctrine-orm/en/latest/).
  *
  * When used with Symfony or Zend Framework 2, Doctrine's Entity Manager is automatically retrieved from Service Locator.
- * Set up your `functional.suite.yml` like this:
+ * Set up your `Functional.suite.yml` like this:
  *
  * ```yaml
  * modules: