Update section on GraphQlSource.Builder

See gh-154, gh-167

spring-graphql-docs/src/docs/asciidoc/index.adoc

@@ -179,6 +179,48 @@ support for <<execution-reactive-datafetcher>>, <<execution-context>>, and
 
 
 
+[[execution-graphqlsource-schema-resources]]
+==== Schema Resources
+
+`GraphQlSource.Builder` can be configured with one or more `Resource` instances to be
+parsed and merged together. That means schema files can be loaded from just about any
+location. By default, the Spring Boot starter <<boot-graphql-schema,loads schema files>>
+from a well-known classpath location, but you can change that to a location on the file system
+via `FileSystemResource`, to byte content via `ByteArrayResource`, or implement a custom
+`Resource` that loads schema files from a remote location or storage.
+
+
+[[execution-graphqlsource-runtimewiring-configurer]]
+==== `RuntimeWiringConfigurer`
+
+You can add a `RuntimeWiringConfigurer` to `GraphQlSource.Builder` to register:
+
+ - custom scalar types.
+ - a `TypeResolver`, if you need to override the
+   <<execution-graphqlsource-default-type-resolver>> for a type.
+ - a `DataFetcher` for a field, although most applications will simply configure
+   `AnnotatedControllerConfigurer`, which detects annotated, `DataFetcher` handler methods.
+   The Spring Boot starter adds the `AnnotatedControllerConfigurer` by default.
+
+
+[[execution-graphqlsource-default-type-resolver]]
+==== Default `TypeResolver`
+
+`GraphQlSource.Builder` registers `ClassNameTypeResolver` as the default `TypeResolver`
+to use for GraphQL Interfaces and Unions that don't already have such a registration
+through a <<execution-graphqlsource-runtimewiring-configurer>>. The purpose of
+a `TypeResolver` in GraphQL Java is to determine the GraphQL Object type for values
+returned from the `DataFetcher` for a GraphQL Interface or Union field.
+
+`ClassNameTypeResolver` tries to match the simple class name of the value to a GraphQL
+Object Type and if it is not successful, it also navigates its super types including
+base classes and interfaces, looking for a match. `ClassNameTypeResolver` provides an
+option to configure a name extracting function along with `Class` to GraphQL Object type
+name mappings that should help to cover more corner cases.
+
+
+
+
 [[execution-reactive-datafetcher]]
 === Reactive `DataFetcher`