Added a description README.md for libraries (#3349)

libraries/README.md

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+# ESP32 Libraries
+
+arduino-esp32 includes libraries for Arduino compatibility along with some object wrappers around hardware specific devices.  Examples are included in the examples folder under each library folder.  The ESP32 includes additional examples which need no special drivers.
+
+### ArduinoOTA
+  Over The Air firmware update daemon.  Use espota.py to upload to the device.
+
+### AsyncUDP
+  Asynchronous task driven UDP datagram client/server
+
+### AzureIoT
+  Library to interact with Microsoft Azure IoT services
+
+### BLE
+  Bluetooth Low Energy v4.2 client/server framework
+
+### BluetoothSerial
+  Serial to Bluetooth redirection server
+
+### DNSServer
+  A basic UDP DNS daemon (includes captive portal demo)
+
+### EEPROM
+  Arduino compatibility for EEPROM (using flash)
+
+### ESP32
+  Additional examples
+  * AnalogOut
+  * Camera
+  * ChipID
+  * DeepSleep
+  * ESPNow
+  * FreeRTOS
+  * GPIO
+  * HallSensor
+  * I2S
+  * ResetReason
+  * RMT
+  * Time
+  * Timer
+  * Touch
+
+### ESPmDNS
+  mDNS service advertising
+
+### FFat
+  FAT indexed filesystem on SPI flash
+
+### FS
+  Filesystem virtualization framework
+
+### HTTPClient
+  A simple HTTP client, compatible with WiFiClientSecure
+
+### HTTPUpdate
+  Download a firmware update from HTTPd and apply it using Update
+
+### NetBIOS
+  NetBIOS name advertiser
+
+### Preferences
+  Flash keystore using ESP32 NVS
+
+### SD
+  Secure Digital card filesystem using SPI access
+
+### SD_MMC
+  Secure Digital card filesystem using 4-lane access
+
+### SimpleBLE
+  Minimal BLE advertiser
+
+### SPI
+  Arduino compatible Serial Peripheral Interface driver (master only)
+
+### SPIFFS
+  SPI Flash Filesystem (see [spiffs-plugin](https://github.com/me-no-dev/arduino-esp32fs-plugin) to upload to device)
+
+### Ticker
+  A timer to call functions on an interval
+
+### Update
+  Sketch Update using ESP32 OTA functionality
+
+### WebServer
+  A simple HTTP daemon
+
+### WiFi
+  Arduino compatible WiFi driver (includes Ethernet driver)
+
+### WiFiClientSecure
+  Arduino compatible WiFi client object using embedded encryption
+
+### Wire
+  Arduino compatible I2C driver (master only)