Update help message for Windows systems

For windows environment the `--help` output will show :
```
set QBT_NO_SPLASH=1
C:\Program Files\qBittorrent\qbittorrent.exe
```
instead of
```
QBT_NO_SPLASH=1 C:\Program Files\qBittorrent\qbittorrent.exe
```

Fixes #22662.
PR #22695.

src/app/cmdoptions.cpp

@@ -491,6 +491,12 @@ QString makeUsage(const QString &prgName)
 {
     const QString indentation {USAGE_INDENTATION, u' '};
 
+#if defined(Q_OS_WIN)
+    const QString noSplashCommand = u"set QBT_NO_SPLASH=1 && " + prgName;
+#else
+    const QString noSplashCommand = u"QBT_NO_SPLASH=1 " + prgName;
+#endif
+
     const QString text = QCoreApplication::translate("CMD Options", "Usage:") + u'\n'
         + indentation + prgName + u' ' + QCoreApplication::translate("CMD Options", "[options] [(<filename> | <url>)...]") + u'\n'
 
@@ -542,7 +548,7 @@ QString makeUsage(const QString &prgName)
                                 "'parameter-name', environment variable name is 'QBT_PARAMETER_NAME' (in upper "
                                 "case, '-' replaced with '_'). To pass flag values, set the variable to '1' or "
                                 "'TRUE'. For example, to disable the splash screen: "), 0) + u'\n'
-        + u"QBT_NO_SPLASH=1 " + prgName + u'\n'
+        + noSplashCommand + u'\n'
         + wrapText(QCoreApplication::translate("CMD Options", "Command line parameters take precedence over environment variables"), 0) + u'\n';
 
     return text;