Update EIP-6120: add Native Token Transfer section

Merged by EIP-Bot.

Author: Zergity

EIPS/eip-6120.md

@@ -177,7 +177,13 @@ interface IUniversalTokenRouter {
 }
 ```
 
-See [Discard Payment](#discard-payment-1) in **Security Considerations** for an important security note.
+Please refer to the [Discard Payment](#discard-payment-1) section in the **Security Considerations** for an important security note.
+
+### Native Token Tranfer
+
+The `UTR` SHOULD have a `receive()` function for user execution logic that requires transferring ETH in. The `msg.value` transferred into the router can be spent in multiple inputs across different actions. While the caller takes full responsibility for the movement of `ETH` in and out of the router, the `exec` function SHOULD refund any remaining `ETH` before the function ends.
+
+Please refer to the [Reentrancy](#reentrancy) section in the **Security Considerations** for information on reentrancy risks and mitigation.
 
 ### Usage Examples