Add 'introspectionFromSchema' utility function

Based on graphql#1114 by @mjmahone

Author: IvanGoncharov

src/index.js

@@ -309,6 +309,8 @@ export {
   introspectionQuery,
   // Gets the target Operation from a Document
   getOperationAST,
+  // Convert a GraphQLSchema to an IntrospectionQuery
+  introspectionFromSchema,
   // Build a GraphQLSchema from an introspection result.
   buildClientSchema,
   // Build a GraphQLSchema from a parsed GraphQL Schema language AST.

src/utilities/index.js

@@ -41,6 +41,9 @@ export type {
 // Gets the target Operation from a Document
 export { getOperationAST } from './getOperationAST';
 
+// Convert a GraphQLSchema to an IntrospectionQuery
+export { introspectionFromSchema } from './introspectionFromSchema';
+
 // Build a GraphQLSchema from an introspection result.
 export { buildClientSchema } from './buildClientSchema';