add callout

Author: youssefea

docs/base-account/improve-ux/spend-permissions.mdx

@@ -11,6 +11,10 @@ After the user signs the permission, the `spender` can initiate transfers within
 
 Read more about the Spend Permission Manager contract and supported chains on [GitHub](https://github.com/coinbase/spend-permissions).
 
+<Callout type="info">
+  Spend Permissions are currently not available on Base App Mini Apps.
+</Callout>
+
 ## Usage
 
 ### Request a Spend Permission