docs/esp8266: Add ESP8266 tutorial.

docs/esp8266/tutorial/intro.rst

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+Introduction to MicroPython on the ESP8266
+==========================================
+
+Using MicroPython is a great way to get the most of your ESP8266 board.  And
+vice versa, the ESP8266 chip is a great platform for using MicroPython.  This
+tutorial will guide you through setting up MicroPython, getting a prompt, using
+WebREPL, connecting to the network and communicating with the Internet, using
+the hardware peripherals, and controlling some external components.
+
+Let's get started!
+
+Requirements
+------------
+
+The first thing you need is a board with an ESP8266 chip.  The MicroPython
+software supports the ESP8266 chip itself and any board should work.  The main
+characteristic of a board is how much flash it has, how the GPIO pins are
+connected to the outside world, and whether it includes a built-in USB-serial
+convertor to make the UART available to your PC.
+
+The minimum requirement for flash size is 512k.  A board with this amount of
+flash will not have room for a filesystem, but otherwise is fully functional.
+If your board has 1Mbyte or more of flash then it will support a filesystem.
+
+Names of pins will be given in this tutorial using the chip names (eg GPIO0)
+and it should be straightforward to find which pin this corresponds to on your
+particular board.
+
+Powering the board
+------------------
+
+If your board has a USB connector on it then most likely it is powered through
+this when connected to your PC.  Otherwise you will need to power it directly.
+Please refer to the documentation for your board for further details.
+
+Deploying the firmware
+----------------------
+
+The very first thing you need to do is put the MicroPython firmware (compiled
+code) on your ESP8266 device.  There are two main steps to do this: first you
+need to put your device in boot-loader mode, and second you need to copy across
+the firmware.  The exact procedure for these steps is highly dependent on the
+particular board and you will need to refer to its documentation for details.
+
+If you have a board that has a USB connector, a USB-serial convertor, and has
+the DTR and RTS pins wired in a special way then deploying the firmware should
+be easy as all steps can be done automatically.  Boards that have such features
+include the Adafruit Feather HUZZAH and NodeMCU boards.
+
+For best results it is recommended to first erase the entire flash of your
+device before putting on new MicroPython firmware.
+
+Currently we only support esptool.py to copy across the firmware.  You can find
+this tool here: `<https://github.com/themadinventor/esptool/>`__ .  Any other
+flashing program should work, so feel free to try them out, or refer to the
+documentation for your board to see its recommendations.
+
+Using esptool.py you can erase the flash with the command::
+
+    esptool.py --port /dev/ttyUSB0 erase_flash
+
+And then deploy the new firmware using::
+
+    esptool.py --port /dev/ttyUSB0 --baud 460800 write_flash --flash_size=8m 0 mp-esp8266-firmware.bin
+
+You might need to change the "port" setting to something else relevant for your
+PC.  You may also need to reduce the baudrate if you get errors when flashing
+(eg down to 115200).
+
+If you have a NodeMCU board, you may need to use the following command to deploy
+the firmware (note the "-fm dio" option)::
+
+    esptool.py --port /dev/ttyUSB0 --baud 460800 write_flash --flash_size=8m -fm dio 0 mp-esp8266-firmware.bin
+
+If the above commands run without error then MicroPython should be installed on
+your board!
+
+Serial prompt
+-------------
+
+Once you have the firmware on the device you can access the REPL (Python prompt)
+over UART0 (GPIO1=TX, GPIO3=RX), which might be connected to a USB-serial
+convertor, depending on your board.  The baudrate is 115200.  The next part of
+the tutorial will discuss the prompt in more detail.
+
+WiFi
+----
+
+After a fresh install and boot the device configures itself as a WiFi access
+point (AP) that you can connect to.  The ESSID is of the form MicroPython-xxxxxx
+where the x's are replaced with part of the MAC address of your device (so will
+be the same everytime, and most likely different for all ESP8266 chips).  The
+password for the WiFi is micropythoN (note the upper-case N).  Its IP address
+will be 192.168.4.1 once you connect to its network.  WiFi configuration will
+be discussed in more detail later in the tutorial.