added command to build sd card from dev branch

README.md

@@ -290,6 +290,10 @@ The whole build process takes a while. At the end the LCD drivers get installed
 
 *Note: If you plan to use your self build sd card as a MASTER copy to backup image and distribute it. Use a smaller 8GB card for that. This way its ensured that it will fit on every 16 GB card recommended for RaspiBlitz later on.*
 
+And if you are a developer - to build a sd card from the dev-branch use this command to execute:
+
+`wget https://raw.githubusercontent.com/rootzoll/raspiblitz/dev/build.sdcard/raspbianStretchDesktop.sh && sudo bash raspbianStretchDesktop.sh 'dev'`
+
 ## Update to a new SD Card Release
 
 At the beginning of this README you can find the newest SD card we provide. Or you can build the newest SD card image yourself like in the chapter above. The SD card image is used to setup a fresh install of the RaspiBlitz. So what to do if you already have an older version running and you want to upgrade?