Make missing limactl a critical error

For now, maybe offer hints on how to install ?

Presumably user is able to find `brew install`

main.cpp

@@ -53,6 +53,7 @@
 #ifndef QT_NO_SYSTEMTRAYICON
 
 #include <QMessageBox>
+#include <QStandardPaths>
 #include "window.h"
 
 int main(int argc, char *argv[])
@@ -71,6 +72,13 @@ int main(int argc, char *argv[])
                                           "on this system."));
         return 1;
     }
+    QString program = QStandardPaths::findExecutable("limactl");
+    if (program.isEmpty()) {
+        QMessageBox::critical(0, QObject::tr("Lima"),
+                              QObject::tr("I couldn't find limactl in PATH "
+                                          "on this system."));
+        return 1;
+    }
     QApplication::setQuitOnLastWindowClosed(false);
 
     Window window;