message: [Doc] Document custom fee save in the DB
diff: @@ -168,6 +168,9 @@ The p2p alert system has been removed in [#1372](https://github.com/PIVX-Project
  Addresses in the dropdown of the "Send Transaction" and "Send Delegation" widgets are now automatically sorted by label with ascending order ([#1393](https://github.com/PIVX-Project/PIVX/pull/1393)).
  +**Custom Fee**: The custom fee selected when sending a transaction is now saved in the wallet database and persisted across multiple sends and wallet's restarts ([#1406](https://github.com/PIVX-Project/PIVX/pull/1406)).
  +
  +
  ### RPC/REST
  