docs: explain how to use spaces to indent

Author: rgomezcasas

README.md

@@ -47,7 +47,13 @@
 
 - Lints PHP using PSR-12
 - Extends some config (you can see all the rules [here](src/coding_style.php))
-- Use tabs to indent ([reason](https://www.youtube.com/watch?v=yD2T42zsP7c))
+- Use tabs to indent ([reason](https://www.youtube.com/watch?v=yD2T42zsP7c)). If you want to use spaces, you can add the
+  following line at the end of your `ecs.php`:
+    ```php
+    use Symplify\EasyCodingStandard\ValueObject\Option;
+
+	$ecsConfig->indentation(Option::INDENTATION_SPACES);
+    ```
 
 ## 📦 How to release a new version
 

src/coding_style.php

@@ -52,6 +52,7 @@
 use Symplify\CodingStandard\Fixer\LineLength\LineLengthFixer;
 use Symplify\CodingStandard\Fixer\Strict\BlankLineAfterStrictTypesFixer;
 use Symplify\EasyCodingStandard\Config\ECSConfig;
+use Symplify\EasyCodingStandard\ValueObject\Option;
 use Symplify\EasyCodingStandard\ValueObject\Set\SetList;
 
 return static function (ECSConfig $ecsConfig): void {
@@ -123,5 +124,5 @@
 	$ecsConfig->ruleWithConfiguration(PhpUnitMethodCasingFixer::class, ['case' => PhpUnitMethodCasingFixer::SNAKE_CASE]);
 	$ecsConfig->ruleWithConfiguration(OrderedTypesFixer::class, ['null_adjustment' => 'always_last']);
 
-	$ecsConfig->indentation('tab');
+	$ecsConfig->indentation(Option::INDENTATION_TAB);
 };