added ESP8266 code

tools/esp8266/README.md

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+## OVERVIEW
+
+This code was tested on a ESP8266 - ESP-07 module. Many parts of the code are based on 'Hubi's code, which can be found here: <https://www.mikrocontroller.net/topic/525778?page=3#7033371>
+
+The NRF24L01+ radio module is connected to the standard SPI pins. Additional there are 3 pins, which can be set individual:
+
+- IRQ - Pin 4
+- CE - Pin 5
+- CS - Pin 15
+
+
+## Compile
+
+This code can be compiled using Arduino. The settings were:
+
+- Board: Generic ESP8266 Module
+- Flash-Size: 1MB (FS: none, OTA: 502kB)
+
+
+## Flash ESP with firmware
+
+1. flash the ESP with the compiled firmware using the UART pins or any preinstalled firmware with OTA capabilities
+2. repower the ESP
+3. the ESP will start as access point (AP) if there is no network config stored in its eeprom
+4. connect to the AP, you will be forwarded to the setup page
+5. configure your WiFi settings, save, repower
+6. check your router for the IP address of the module
+
+
+## Usage
+
+Connect the ESP to power and to your serial console. The webinterface is currently only used for OTA and config.
+The serial console will print all information which is send and received.
+
+
+## Known Issues
+
+- only command 0x81 is received
+
+
+## USED LIBRARIES
+
+- `Time`
+- `RF24`
+