Fix incorrect tab mentioned for frontend app registration (microsoft#248

)

### Motivation and Context
This fixes incorrect documentation when trying to setup the azure
application permissions for the frontend.

### Description
When adding the api permissions for the first time to the frontend, the
"My APIs" will actually be empty:

![image](https://github.com/microsoft/chat-copilot/assets/13119203/a1a6a1ea-8295-4f59-9a59-94657249bca2)
(you can ignore the "hidden" - thats another app we have developed)

Instead the previously created exposure of the backend can only be found
in the "APIs my organization uses" tab:

![image](https://github.com/microsoft/chat-copilot/assets/13119203/9ee78095-7b20-4ad5-a920-9b4ab6a7e607)

README.md

@@ -181,7 +181,7 @@ By default, Chat Copilot runs locally without authentication, using a guest user
 
    3. Click _Add a permission_
 
-   4. Select the tab _My APIs_
+   4. Select the tab _APIs my organization uses_
 
    5. Choose the app registration representing the web api backend