boards/thingy52: Add description and more precise flashing instructions

boards/thingy52/doc.txt

@@ -3,8 +3,39 @@
 @ingroup     boards
 @brief       Support for the Nordic Thingy:52 board
 
+## Overview
+The Nordic Thingy:52 is a battery powered platform with Bluetooth and NFC
+radio, a wide range of sensors and some output capabilities.
+
+Components:
+
+- nRF52832 main controller (providing Bluetooth and NFC)
+- an LIS2DH12 low-power three-axis linear accelerometer
+- an MPU-9250 nine-axis motion sensor
+- an LPS22HB air pressure and temperatur sensor
+- an HTS221 air temperature and humidity sensor
+- a BH1745NUC color sensor
+- a CCS811 gas sensor
+- an MP34DB02 digital microphone
+- a speaker
+- two RGB LED channels: one LED pair in the light well, and one RGB LED to assist the light sensor
+- a button
+- an XC6804A4E1 battery charge controller (providing charge error indication)
+- USB power supply and battery voltage sensing
+- four DMN3190LDW MOSFETs
+
+Note that at the moment, only the button and a single UART (at P6) are supported in RIOT.
+
+## Links
+
+- [Device description](https://infocenter.nordicsemi.com/topic/ug_thingy52/UG/thingy52/intro/frontpage.html)
+
 ## Flash the board
 
+The board can be flashed using an external programmer on its 10-pin debug port P9.
+
 See the `Flashing` section in @ref boards_common_nrf52.
 
+Its over-the-air bootloading mechanism is currently not supported in RIOT.
+
  */