[doc/log] Fix markdown syntax and line terminate LogPrint

- Fix doxygen comment for payTxFee
- [doc] Fix markdown
- Make sure LogPrintf strings are line-terminated

Github-Pull: #7617
Rebased-From: fa06ce0949 fa97f95c15 fa26652459

src/wallet/wallet.cpp

@@ -33,9 +33,7 @@
 
 using namespace std;
 
-/**
- * Settings
- */
+/** Transaction fee set by the user */
 CFeeRate payTxFee(DEFAULT_TRANSACTION_FEE);
 CAmount maxTxFee = DEFAULT_TRANSACTION_MAXFEE;
 unsigned int nTxConfirmTarget = DEFAULT_TX_CONFIRM_TARGET;