Improve documentation for ast_from_value

Author: Cito

src/graphql/utilities/ast_from_value.py

@@ -34,7 +34,12 @@
 
 
 def ast_from_value(value: Any, type_: GraphQLInputType) -> Optional[ValueNode]:
-    """Produce a GraphQL Value AST given a Python value.
+    """Produce a GraphQL Value AST given a Python object.
+
+    This function will match Python/JSON values to GraphQL AST schema format by using
+    the suggested GraphQLInputType. For example::
+
+        ast_from_value('value', GraphQLString)
 
     A GraphQL type must be provided, which will be used to interpret different Python
     values.