added: instructions for creating img file

README.md

@@ -12,6 +12,21 @@ Before executing this script following steps must be executed:
 4. Execute this script `bash <(curl -sL https://kiosk-rpi-files.s3.eu-central-1.amazonaws.com/prepare-kiosk.sh)`. After script is completed the RPi will reboot and start with kiosk client
 5. In case you want to exit kiosk mode: either connect keyboard and enter `ctrl`, `alt` and `backspace` keys combination or connect via SSH
 
+### Generate .img from SD card
+
+In order to reproduce multiple identical Kiosk devices you can create an `.img` backup file, and use it to flash the device.  
+
+1. Attach the source SD card that you want to clone
+2. List the local drives mounted on your computer:
+    ```bash
+    diskutil list
+    ```
+3. Create the gzipped `img` file:
+    ```bash
+    sudo dd if=/dev/disk5 bs=1m | gzip > ~/workspace/kiosk-v0.0.5.gz
+    ```
+
+
 ### Known Issues
 
   * **none**