[UPGRADE] Add Rector 0.9 upgrade docs (#4907)

UPGRADE_09.md

@@ -0,0 +1,61 @@
+# How to Upgrade From Rector 0.8 to 0.9
+
+## In Symfony project, clear `config/bundles.php`
+
+- drop `ComposerJsonManipulatorBundle` class
+- drop `ConsoleColorDiffBundle` class
+
+## `rector.php`
+
+Since Rector 0.9 we switched from internal skipping to [`symplify/skipper` package](https://tomasvotruba.com/blog/2020/12/10/new-in-symplify-9-skipper-skipping-files-and-rules-made-simple/). Now there is only one `Option::SKIP` parameter to handle both paths and classes.
+
+Replace deprecated `Option::EXCLUDE_RECTORS` parameters with `Option::SKIP`:
+
+```diff
+ use Rector\Core\Configuration\Option;
+ use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
+
+ return static function (ContainerConfigurator $containerConfigurator): void {
+     $parameters = $containerConfigurator->parameters();
+
+-    $parameters->set(Option::EXCLUDE_RECTORS, [
++    $parameters->set(Option::SKIP, [
+         SomeRector::class,
+     ]);
+ };
+```
+
+Replace deprecated `Option::EXCLUDE_PATHS` parameters with `Option::SKIP`:
+
+```diff
+ use Rector\Core\Configuration\Option;
+ use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
+
+ return static function (ContainerConfigurator $containerConfigurator): void {
+     $parameters = $containerConfigurator->parameters();
+
+-    $parameters->set(Option::EXCLUDE_PATHS, [
++    $parameters->set(Option::SKIP, [
+         __DIR__ . '/SomePath,
+     ]);
+ };
+```
+
+Be sure to have **exactly 1** `Option::SKIP` in the end, as the Symfony parameters are not merged, but overridden:
+
+```diff
+ use Rector\Core\Configuration\Option;
+ use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
+
+ return static function (ContainerConfigurator $containerConfigurator): void {
+     $parameters = $containerConfigurator->parameters();
+
+     $parameters->set(Option::SKIP, [
+         SomeRector::class,
+-    ]);
+-
+-    $parameters->set(Option::SKIP, [
+         __DIR__ . '/SomePath,
+     ]);
+ };
+```