[3.x.x/docs] fixing documentation on adding types to generator (#961)

Author: dariuszkuc

docs/schema-generator/customizing-schemas/advanced-features.md

@@ -8,25 +8,24 @@ title: Advanced Features
 There are a couple ways you can add more types to the schema without having them be directly consumed by a type in your schema.
 This may be required for [Apollo Federation](federated/apollo-federation), or maybe adding other interface implementations that are not picked up.
 
+### `SchemaGenerator::generateSchema`
+
+When generating a schema you can optionally specify additional types and input types to be included in the schema. This will
+allow you to link to those types from your custom `SchemaGeneratorHooks` implementation using GraphQL reference instead of
+manually creating the underlying GraphQL type.
+
+```kotlin
+val myConfig = SchemaGeneratorConfig(supportedPackages = listOf("com.example"))
+val generator = SchemaGenerator(myConfig)
+
+val schema = generator.generateSchema(
+        queries = myQueries,
+        additionalTypes = setOf(MyCustomObject::class.createType()),
+        additionalInputTypes = setOf(MyCustomInputObject::class.createType())
+)
+```
 
 ### `SchemaGenerator::addAdditionalTypesWithAnnotation`
 
 This method is protected so if you override the `SchemaGenerator` used you can call this method to add types that have a specific annotation.
 You can see how this is used in `graphql-kotlin-federation` as [an example](https://github.com/ExpediaGroup/graphql-kotlin/blob/master/graphql-kotlin-federation/src/main/kotlin/com/expediagroup/graphql/federation/FederatedSchemaGenerator.kt).
-
-### `SchemaGenerator::generateAdditionalTypes`
-
-This method is called by `SchemaGenerator::get` after all the queries, mutations, and subscriptions have been generated and it is going to add all the types saved in an internal set that were not generated by reflection.
-To change the behaviour, you can update the set and then call the super method with the new value.
-
-Example:
-
-```kotlin
-class CustomSchemaGenerator(config: SchemaGeneratorConfig) : SchemaGenerator(config) {
-
-    override fun generateAdditionalTypes(types: Set<KType>): Set<GraphQLType> {
-        val newTypes = types.toMutableSet().add(MyNewType()::class.createType())
-        return super.generateAdditionalTypes(newTypes)
-    }
-}
-```