Add notes for ESP8266 version

NOTES

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+Arduino IDE with ESP8266 support
+================================
+
+This is an early beta. Things might not work as expected, please do report any bugs you find.
+
+What works
+----------
+
+- pinMode, digitalRead, digitalWrite
+- analogRead
+- shiftIn, shiftOut
+- millis, micros, delay, delayMicroseconds
+- yield (call that once in a while in long loops; delay() works as well)
+- Serial
+	Only 8n1 is supported right now. flush() doesn't work, and there is no propper TX buffer.
+	When sending long strings (>128 chars at a time) something might get lost.
+	There will be some diagnostic output from WiFi libraries unless you call Serial.begin.
+
+- EEPROM
+	This is a bit different from standard EEPROM class. You need to call EEPROM.begin(size)
+	before you start reading or writing, size being the number of bytes you want to use.
+	EEPROM.write does not write to flash immediately, instead you must call EEPROM.commit()
+	whenever you wish to save changes to flash. EEPROM.end() will also commit, and will
+	release the RAM copy of EEPROM contents.
+
+- I2C (Wire library)
+	Only master mode works, and I haven't tested if Wire.setClock gives correct frequency.
+	Before using I2C, you need to set pins you will use for SDA and SCL by calling
+	Wire.pins(int sda, int scl), i.e. Wire.pins(0, 2); on ESP-01.
+
+- WiFi (ESP8266WiFi library)
+	This is mostly similar to WiFi shield library. Differences include:
+		* WiFi.mode(m): set mode to WIFI_AP, WIFI_STA, or WIFI_AP_STA.
+		* WiFi.softAP(ssid) or WiFi.softAP(ssid, passphrase) to set up an AP.
+		* WiFi.macAddress(mac) is for STA, WiFi.softAPmacAddress(mac) is for AP.
+		* WiFi.localIP() is for STA, WiFi.softAPIP() is for AP.
+		* WiFi.RSSI() doesn't work
+		* WiFi.scanNetworks() doesn't work yet
+	WiFiServer and WiFiClient behave mostly the same way as with WiFi shield library.
+
+- Other libraries that don't rely on low-level access to AVR registers.
+
+- Upload via serial port
+	Select "esptool" as a programmer, and pick the correct serial port.
+	You need to put ESP8266 into bootloader mode before uploading code (pull GPIO0 low and toggle power).
+
+What is not done yet
+--------------------
+
+- pin interrupts (attachInterrupt, detachInterrupt)
+- analogWrite (PWM)
+- pulseIn, pulseOut
+- SPI
+- UDP
+- I2C slave mode
+- Serial modes other than 8n1
+- Serial TX buffer
+- WiFi.scanNetworks
+- WiFi.RSSI
+- Upload sketches via WiFi
+- Samples for all the libraries
+
+
+License and credits
+-------------------
+
+Arduino is licensed under GPL, with Arduino core libraries licensed under LGPL.
+This build includes an xtensa gcc toolchain, which is also under GPL.
+Espressif SDK included in this build is under Espressif Public License.
+
+ESP8266 port contributed by Ivan Grokhotkov, igrokhotkov at gmail dot com.
+Drop me a line if you find some bugs not mentioned here!
+