docs: modified mailu API_KEY note.

README.md

@@ -35,7 +35,8 @@ const mailuClient = new MailuClient(endpoint, apiKey);
 })();
 
 ```
-[Your API key](https://mailu.io/master/api.html) is stored within the mailu directory on your system, contained within the .env environment file.
+##### Important Note
+Your API key is stored within the `mailu` directory on your system, contained within the `.env` environment file. Reference the Mailu documentation for specifics.
 
 ## Sections
 * **MailuClient**
@@ -122,4 +123,4 @@ Methods for managing Mailu users.
 * **createUser(body)** -  Creates a new user.
 * **updateUser(email, body)** - Updates a user.
 * **getUser(email)** - Retrieves details of a user.
-* **deleteUser(email)** - Deletes a user. 
+* **deleteUser(email)** - Deletes a user.