esp8266: Update flashing instructions in README.

esp8266/README.md

@@ -32,7 +32,8 @@ Build instructions
 The tool chain required for the build is the OpenSource ESP SDK, which can be
 found at <https://github.com/pfalcon/esp-open-sdk>.  Clone this repository and
 run `make` in its directory to build and install the SDK locally.  Make sure
-to add toolchain bin directory to your PATH.
+to add toolchain bin directory to your PATH.  Read esp-open-sdk's README for
+additional important information on toolchain setup.
 
 Add the external dependencies to the MicroPython repository checkout:
 ```bash
@@ -46,22 +47,26 @@ Then, to build MicroPython for the ESP8266, just run:
 $ cd esp8266
 $ make
 ```
-This should produce binary images in the `build/` subdirectory.  To flash them
-to your ESP8266, use:
+This will produce binary images in the `build/` subdirectory. If you install
+MicroPython to your module for the first time, or after installing any other
+firmware, you should erase flash completely:
+
+```
+esptool.py --port /dev//ttyXXX erase_flash
+```
+
+Erase flash also as a troubleshooting measure, if a module doesn't behave as
+expected.
+
+To flash MicroPython image to your ESP8266, use:
 ```bash
 $ make deploy
 ```
 This will use the `esptool.py` script to download the images.  You must have
-your ESP module in the bootloader, and connected to a serial port on your PC.
+your ESP module in the bootloader mode, and connected to a serial port on your PC.
 The default serial port is `/dev/ttyACM0`.  To specify another, use, eg:
 ```bash
 $ make PORT=/dev/ttyUSB0 deploy
 ```
 
-The images that are built are:
-- `firmware.elf-0x00000.bin`: to be flashed at 0x00000
-- `firmware.elf-0x10000.bin`: to be flashed at 0x10000
-
-There is also a combined image, made up of the above 2 binary files with the
-appropriate padding:
-- `firmware-combined.bin`: to be flashed at 0x00000
+The image produced is `firmware-combined.bin`, to be flashed at 0x00000.