rpc: Document that enabling trace-level logging is unsafe

src/rpc/server.cpp

@@ -255,6 +255,9 @@ UniValue setlogfilter(const UniValue& params, bool fHelp)
             + strprintf("\n    %s", LogConfigFilter()) + "\n"
             "\nPassing a valid filter here will replace the existing filter.\n"
             "Passing an empty string will reset the filter to the default.\n"
+            "\nNote that enabling trace-level events should always be considered\n"
+            "unsafe, as they can result in sensitive information like decrypted\n"
+            "notes and private keys being printed to the log output.\n"
             "\nArguments:\n"
             "1. newFilterDirectives (string, required) The new log filter.\n"
             "\nExamples:\n"