Update README.md

README.md

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 # Shelly convert to HAA
 This guide explains how to convert Shelly ESP32 and ESP32-C3 driven devices to [HAA firmware](https://github.com/RavenSystem/esp-homekit-devices/wiki)
 
-## :warning: **There is no way back to Shelly firmware if the process has been initiated!**
+## :warning: **There is no way back to Shelly firmware if the new ZIP file has been uploaded!**
+Shelly bootloader will be replaced with a standard ESP-IDF bootloader, avoiding to back to original firmware. To back to Shelly firmware or to recover it if something goes wrong, a wired connection to a PC using a FTDI adapter is needed.
 
 ## Requisites
 - Download corresponding ZIP file from [Releases](https://github.com/RavenSystem/mgos32toHAA/releases).