added readme links

packages/medusa-plugin-mailchimp/README.md

@@ -2,12 +2,14 @@
 
 Mailchimp plugin for Medusa that supports newsletter subscriptions.
 
-## Plugin Options
+Learn more about how you can use this plugin in the [documentaion](https://docs.medusajs.com/add-plugins/mailchimp).
 
-```
+## Options
+
+```js
 {
-  api_key: [your mailchimp api key] (required),
-  newsletter_list_id: ["123456789"] (required)
+  api_key: "MAILCHIMP_API_KEY",
+  newsletter_list_id: ["123456789"]
 }
 ```