Add documentation about parsers configuration

Author: a-melnikov

README.md

@@ -90,6 +90,7 @@ Documentation
 - [Errors handling](docs/error-handling/index.md)
 - [Events](docs/events/index.md)
 - [Profiler](docs/profiler/index.md)
+- [Tune configuration](docs/tune_configuration.md)
 
 Talks and slides to help you start
 ----------------------------------

docs/tune_configuration.md

@@ -0,0 +1,22 @@
+Tune configuration
+==================
+
+Custom GraphQl configuration parsers
+------------------------------------
+
+You can configure custom GraphQl configuration parsers.
+Your parsers MUST implement at least `\Overblog\GraphQLBundle\Config\Parser\ParserInterface`
+and optionally `\Overblog\GraphQLBundle\Config\Parser\PreParserInterface` when required.
+
+Default values will be applied when omitted.
+
+```yaml
+overblog_graphql:
+    # ...
+    parsers:
+        yaml: 'Overblog\GraphQLBundle\Config\Parser\YamlParser'
+        graphql: 'Overblog\GraphQLBundle\Config\Parser\GraphQLParser'
+        annotation: 'Overblog\GraphQLBundle\Config\Parser\AnnotationParser'
+        attribute: 'Overblog\GraphQLBundle\Config\Parser\AttributeParser'
+    # ...
+```