Adding default parameters to start script

staging/dev/start_vm.sh

 #!/bin/sh
 
-IMG=$1
-echo "Mount $IMG"
+# Default parameters
+if [ $1 ];then
+    IMG=$1;
+else
+    echo "\nYou must provide the raspberry pi image as first parameter\n";
+    exit;
+fi
+
+if [ $2 ];then
+    KERNEL=$2;
+else
+    KERNEL="rpi-20200922/kernel-qemu-5.4.51-buster"
+fi
+
+if [ $3 ];then
+    DTB=$3;
+else
+    DTB="rpi-20200922/versatile-pb-buster-5.4.51.dtb"
+fi
+
+# Start qemu
 qemu-system-arm \
     -kernel rpi-20200922/kernel-qemu-5.4.51-buster \
     -dtb rpi-20200922/versatile-pb-buster-5.4.51.dtb \