Tweak README to include new configuration details for Symfony 4, tweak variable name

README.md

@@ -28,30 +28,40 @@ ensures that application behaviour will not be affected by stateful services.
             FriendsOfBehat\SymfonyExtension: ~
     ```
 
-    **Symfony 3 configuration**
+3. Good luck & have fun!
+
+    
+## Configuration
+
+SymfonyExtension provides kind of autoconfiguration feature.
+When none explicit configuration is set, we will set for You sane default that will get you running fast.
+
+**Default Symfony 3 configuration**
 
 ```
 FriendsOfBehat\SymfonyExtension:
     kernel:
-            bootstrap: 'var/bootstrap.php.cache'
+        bootstrap: 'app/autoload.php' # you may want to use var/bootstrap.php.cache instead
         path: app/AppKernel.php
         class: 'AppKernel'
         env: test
         debug: true
 ```
 
-    **Symfony 4 configuration**
+**Default Symfony 4 configuration**
 
 ```
 FriendsOfBehat\SymfonyExtension:
     # .env.dist file will be used if .env file does not exist
     env_file: .env
     kernel:
-            class: 'MyTrip\Kernel'
+        bootstrap: ~
         path: src/Kernel.php
-            debug: true
+        class: 'App\Kernel'
+        env: test # When explicitly set, will override APP_ENV loaded from env_file file
+        debug: true  # When explicitly set, will override APP_DEBUG loaded from env_file file
 ```
 
-    Symfony 4 does not have bootstrap file anymore and the environment is configured in the .env file.
+Symfony 4 is detected, based on the existence of `src/Kernel.php` file, so if you did not migrate to new Symfony structure yet; you need to set those values yourself.
 
-3. Good luck & have fun!
+Of course, you can always change each of those settings.

src/ServiceContainer/SymfonyExtension.php

@@ -169,8 +169,8 @@ final class SymfonyExtension implements Extension
 
         $defaults = self::SYMFONY_DEFAULTS;
 
-        $symfonyFlexKernelPath = sprintf('%s/%s', $container->getParameter('paths.base'), self::SYMFONY_4_DEFAULTS['kernel']['path']);
+        $symfony4KernelPath = sprintf('%s/%s', $container->getParameter('paths.base'), self::SYMFONY_4_DEFAULTS['kernel']['path']);
-        if (file_exists($symfonyFlexKernelPath)) {
+        if (file_exists($symfony4KernelPath)) {
             $defaults = self::SYMFONY_4_DEFAULTS;
         }