[mihome] Update README.md (openhab#7281)

Signed-off-by: Stefan Schmidhammer <byteterra@hotmail.com>
Signed-off-by: CSchlipp <christian@schlipp.de>

bundles/org.openhab.binding.mihome/README.md

@@ -45,6 +45,17 @@ After setup, you can disconnect the gateway from the internet to keep your senso
 
 * Enable developer mode of your gateway:
 
+ 1. Select your Gateway in the MiHome app
+ 2. Go to the "..." menu on the top right corner and click "About"
+ 3. You now see two options "Smart Home Kit Forum" and "Gameplay Tutorial". Tap 5 times below the "Gameplay Tutorial" in the empty space (not the button itself) until you enable developer mode
+ 4. You should now have 2 extra options listed: `wireless communication protocol` and `hub info`, it may appear in Chinese
+ 5. Choose `wireless communication protocol`
+ 6. Tap the toggle switch to enable WiFi functions. Note down the developer key (aka password), something like: 91bg8zfkf9vd6uw7
+ 7. Make sure you hit the OK button (to the right of the cancel button) to save your changes
+ 8. Now update the gateway to the latest firmware
+
+* Enable developer mode of your gateway (legacy app):
+
  1. Select your Gateway in the MiHome app
  2. Go to the "..." menu on the top right corner and click "About"
  3. Tap the version number "Plug-in version : 2.XX.X" at the bottom of the screen repeatedly until you enable developer mode