Add symfony 4 configuration loading when bootstrap is null; tweaked formatting, naming, tests and readme

README.md

@@ -62,6 +62,19 @@ FriendsOfBehat\SymfonyExtension:
         debug: true  # When explicitly set, will override APP_DEBUG loaded from env_file 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.
+Symfony 4 is automatically detected, based on the existence of default `src/Kernel.php` kernel file.
+
+If you did not migrate to new Symfony structure yet or you are using custom paths/naming; you need to configure `kernel.boostrap` parameter, to enable default Symfony 4 configuration as shown in the example below:
+
+```
+FriendsOfBehat\SymfonyExtension:
+    # env_file: .env # loaded from the default configuration
+    kernel:
+        bootstrap: ~ # this enables default Symfony 4 configuration
+        path: app/AppKernel.php
+        # class: 'App\Kernel' # loaded from the default configuration
+        # env: test # loaded from the default configuration
+        # debug: true  # loaded from the default configuration
+```
 
 Of course, you can always change each of those settings.