Update wallet12.mdx

docs/pages/use-cases/WalletQueries/wallet12.mdx

@@ -212,6 +212,8 @@ Remember you can also review the results in any Cardano explorer.  The *Cardano
 
 ### 12.3 Collateral input & output 
 
+The collateral mechanism is an important feature that has been designed to ensure successful smart contract execution. You can read more about it in the [documentation](https://docs.cardano.org/about-cardano/learn/collateral-mechanism/).
+
 This query retrieves information about the inputs and outputs associated with our transaction, identified by its hash `52385f2dd6b69eb035474b529249afda132cde54f54c727842393edc51bebb57`. The inputs and outputs are categorized in the results in the 'collateral' column.
 
 ```sql