add readme file.

Author: HirohitoHigashi

samples/HDC1000_Humidity/README.md

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+# Texas Instruments HDC1000
+
+Digital Humidity Sensor with Integrated Temperature Sensor.
+
+https://www.ti.com/product/HDC1000
+
+## Breakout board
+
+AkizukiDenshi AE-HDC1000.
+
+<img src="https://github.com/mrubyc/devkit02/raw/main/samples/HDC1000_Humidity/img/M-08775.jpg">
+
+Connect a grove connector with soldering.
+
+<img src="https://github.com/mrubyc/devkit02/raw/main/samples/HDC1000_Humidity/img/hdc1000_grove.jpg">
+
+
+## Connect to the board.
+
+Connect to the glove I2C connector.
+
+
+## Sample program
+
+1. Using I2C interface.
+2. Reads temperature and humidity about once every second.
+
+## Demo