Instructions to create compressed img

Closes #5

README.md

@@ -474,6 +474,24 @@ sudo systemctl start pio-remote.service
 sudo systemctl status pio-remote.service
 ```
 
+## Create an image of the system
+
+It is a good idea to create an image of your system to flash it back on a fresh SD card if needed. In fact, corruption of cards can happen, so it is recommended to keep an image ready to be transferred to economize some time.
+On a Linux system, plug the SD card and run the following command to create a raw copy:
+```sh
+sudo dd bs=4M if=/dev/mmcblk0 of=~/Documents/raspios-armhf.img conv=fsync
+```
+With `/dev/mmcblk0` the name of the SD card. Feel free to change the name of the image.
+
+By default, dd will make a bit-by-bit image of the SD card, even if a major part is filled with zeroes. To reduce the image size, we can use [PiShrink](https://github.com/Drewsif/PiShrink) to reduce its size:
+```sh
+wget https://raw.githubusercontent.com/Drewsif/PiShrink/master/pishrink.sh
+chmod +x pishrink.sh
+# Install the scripts in the list of binaries to run it directly from cmd-line
+sudo mv pishrink.sh /usr/local/bin
+
+sudo pishrink.sh -az ~/Documents/raspios-armhf.img
+```