[wallet] Add comments for doxygen

src/wallet/wallet.cpp

@@ -1842,6 +1842,7 @@ bool CWallet::CreateTransaction(const vector<CRecipient>& vecSend, CWalletTx& wt
         LOCK2(cs_main, cs_wallet);
         {
             nFeeRet = 0;
+            // Start with no fee and loop until there is enough fee
             while (true)
             {
                 txNew.vin.clear();