Instead of flash0directory, have a NAND subdirectory under PSP, where you can keep flash0, flash1 etc.

Also make it configurable via command line.

Core/CmdLine.cpp

@@ -512,7 +512,6 @@ void CommandLineOptions::ApplyToConfig() const {
 	if (pauseMenuExit.has_value()) {
 		g_Config.bPauseMenuExitsEmulator = pauseMenuExit.value();
 	}
-
 	if (debuggerPort.has_value()) {
 		g_Config.iRemoteISOPort = debuggerPort.value();
 		g_Config.DoNotSaveSetting(&g_Config.iRemoteISOPort);
@@ -551,6 +550,12 @@ void CommandLineOptions::ApplyToConfig() const {
 		CreateSysDirectories();
 	}
 
+	if (nand.has_value()) {
+		// No DoNotSaveSetting() here - memStickDirectory isn't an ordinary setting and never gets
+		// written to ppsspp.ini, since the ini itself lives inside the memory stick directory.
+		g_Config.nandRootDirectory = Path(nand.value());
+	}
+
 	if (resolutionScale.has_value()) {
 		g_Config.iInternalResolution = resolutionScale.value();
 		g_Config.DoNotSaveSetting(&g_Config.iInternalResolution);