add schema submodule README

Author: leebyron

src/language/schema/README.md

@@ -0,0 +1,10 @@
+GraphQL Schema Language
+-----------------------
+
+The `graphql/language/schema` module is responsible for parsing and operating on
+the GraphQL schema definition language.
+
+```js
+import { ... } from 'graphql/language/schema'; // ES6
+var GraphQLSchemaLanguage = require('graphql/language/schema'); // CommonJS
+```