remove useless config and improve mapping need explaination

Author: GregoireHebert

core/getting-started.md

@@ -203,11 +203,11 @@ If and only if you are using the XML or the YAML, you need to tell API Platform
 api_platform:
     mapping:
         paths: 
-            - '%kernel.project_dir%/src/Entity' # default configuration
-            - '%kernel.project_dir%/config/api_platform' # my
+            - '%kernel.project_dir%/src/Entity' # default configuration for annotations
+            - '%kernel.project_dir%/config/api_platform' # yaml or xml directory configuration
 ```
 
-Note that the resources configuration only support the normalization / denormalization context definition in `yaml` and `xml`. To configure the groups of serialization for each attribute, you need to define your groups like you would usually on a standard Symfony project. See the [Symfony doc](https://symfony.com/doc/current/components/serializer.html#attributes-groups).
+Note that the resources configuration only support the normalization / denormalization context definition in `YAML` and `XML`. To configure the groups of serialization for each attribute, you need to define your groups like you would usually on a standard Symfony project. See the [Symfony doc](https://symfony.com/doc/current/components/serializer.html#attributes-groups).
 
 **You're done!**