docs(client): Update setFeeGranter and setFeePayer comments (#22526)

client/tx_config.go

@@ -47,11 +47,17 @@ type (
 		SetSignatures(signatures ...signingtypes.SignatureV2) error
 		SetMemo(memo string)
 		SetFeeAmount(amount sdk.Coins)
+		// SetFeePayer sets the address of who will pay the fees for this transaction.
+		// Note: The fee payer must sign the transaction in addition to any other required signers.
 		SetFeePayer(feePayer sdk.AccAddress)
 		SetGasLimit(limit uint64)
 		SetTimeoutHeight(height uint64)
 		SetTimeoutTimestamp(timestamp time.Time)
 		SetUnordered(v bool)
+		// SetFeeGranter sets the address of the fee granter for this transaction.
+		// A fee granter is an account that has given permission (via the feegrant module)
+		// to pay fees on behalf of another account. Unlike the fee payer, the fee granter
+		// does not need to sign the transaction.
 		SetFeeGranter(feeGranter sdk.AccAddress)
 		AddAuxSignerData(tx.AuxSignerData) error
 	}