recently I purchased this
I could not find any documentation, but I was able to make contact with the seller who linked me to a few sites on how to do the firmware, but it was all in chinese, the one document I was able to translate says this
About using Arduino USB -TTL under no circumstances to flash firmware tutorial (not available in all Arduino Uno Arduino and other single serial device) 2015 -12 -17 v1 by Wang Tongze China, Beijing http://wangtongze.tk
In the case of the non-energized Arduino WiFi ESP8266 WiFi expansion board superimposed on Arduino, will switch to ON DFU
Use jumper RESET (RST) Arduino connected to GND on the power after the dip to ON 1,2 // At this point you can open the Arduino IDE's serial monitor to communicate with ESP8266 Shield, without writing any program to the Arduino board
Open ESP8266 a brush to write the software key and select the port number to Arduino to ESP8266 Shield brush firmware writing operation. Other issues refer to the information package!
still unable to figure this out, if anyone has any info that would be lovely