docs: Add feathersClient to imports in example

Author: marshallswain

docs/api-overview.md

@@ -139,7 +139,7 @@ The following example creates a User class and registers it with the new `makeSe
 
 ```js
 // src/store/services/users.js
-import { makeServicePlugin, BaseModel } from '../feathers-client'
+import feathersClient, { makeServicePlugin, BaseModel } from '../feathers-client'
 
 class User extends BaseModel {
   constructor(data, options) {