[skip ci] readme: fix config reference

Author: mfn

README.md

@@ -233,8 +233,8 @@ the global one.
 The processing of a GraphQL request, henceforth called "execution", flows
 through a set of middelwares.
 
-They can be set on global level via `config.execution_middleware` or per-schema
-via `config.schemas.<yourschema>.execution_middleware`.
+They can be set on global level via `graphql.execution_middleware` or per-schema
+via `graphql.schemas.<yourschema>.execution_middleware`.
 
 By default, the recommended set of middlewares is provided on the global level.