docs(minting): add executor fee details to minting process

Author: fassko

docs/fassets/3-minting.mdx

@@ -93,6 +93,18 @@ This share remains in the agent's underlying account but is not marked as being
 
 This share is minted as FAssets and sent to the [collateral pool](/fassets/collateral#pool-collateral). The percentage of this share is defined by the agent and can be changed by the agent after a delay that provides time for minters to notice the change.
 
+### Executor Fee
+
+To incentivize reliable execution of minting requests, an **executor fee** may be included in the system.  
+The executor is the actor who submits the payment proof to the Asset Manager, finalizing the minting process.
+
+- The executor fee is paid by the minter when minting is executed.
+- This fee is optional and configurable within the system based on chain-specific governance parameters.
+- If set, the fee is denominated in FLR and transferred directly to the executor's address as part of the execution transaction.
+- Executors compete to be the first to execute minting and collect this fee, providing a decentralized execution layer.
+
+This design ensures timely and reliable minting finalization without relying on a centralized party.
+
 ### Trailing Fees
 
 To ensure that agents and collateral pool providers receive steady income, the FAsset system offers an option to enable FAsset token transfer fees, also known as trailing fees.