Added boostrap doc

README.md

@@ -13,13 +13,30 @@ mbed toolchain GCC_ARM
 mbed target NUCLEO_L073RZ
 # set-up the compiler path if needed
 mbed config -G GCC_ARM_PATH /opt/gcc-arm-none-eabi-7-2017-q4-major/bin
-cp mbed_app.json.sample mbed_app.json
-# modify lora.device-eui, lora.application-eui and lora.application-key in mbed_app.json
-# or use the provided script to change them into the binary file
+```
+
+### Bootstrap mode
+
+This mode is used to initialize a mbed NVStore on the flash and store board-specific parameters.
+To compile the bootstrap binary you have to set "mode-bootstrap" to true into mbed_app.json and set
+lorawan EUIs and key.
+
+```
+mbed compile --profile profiles/release.json
+```
+
+Then you can use flash the board and start it. You can check the serial console to see
+
+### Production mode
+
+Just reset "mode-boostrap" to false and compile it (you can delete BUILD folder from previous compilation) :
+
+```
 mbed compile --profile profiles/release.json
 ```
 
-Then you can use stm32flash or - may be better - a stlink interface to copy the generated .bin file onto the RAK811.
+In this mode, lorawan parameters are ignored (because the program get it from the flash) but
+leave it as-is because they are used to determine the stored size ot the euis and key.
 
 ## Notes