Update README.md

Author: huadiweilaoqy

README.md

@@ -1 +1,62 @@
 # Seeed_Arduino_RotaryEncoder
+
+### Introduction
+
+This library support Encoder.
+
+Connect the Encoder to the D2 and D3 pins of the motherboard.You can use other pins if you want.
+
+###  Usage
+
+   1.git clone this resp to your Arduino IDE'S libraries directory.
+
+   2.Run the demo "encoderTest" on examples directory.
+
+### Software usage  
+
+- Install Seeed Arduino RotaryEncoder library to Arduino.  
+
+- Start a project.  
+
+- Create the callback function and set the Encoder pin.(just set SIGA.SIGB pin is equal to SIGA pin plus 1.)
+
+   Usage of the library, see Example encoderTest
+   
+   1. Add headers
+   ```
+      #include "GroveEncoder.h"
+   ```
+   2. Create the callback function.The callback function gets the current Angle and the status of the button press.
+   Define a 'value' to determine whether the Angle value has changed.Define a 'bt_flag' to prevent the button value from being read    more than once.And set 'bt flag' to 1 in the while() function.You can also get the Angle value through the getValue() function.
+   ```
+      int value = 0;
+      int bt_flag = 0;
+      void myCallback(int newValue, bool flag) {
+        if(value != newValue)
+        {
+          value = newValue;
+          Serial.print(newValue, HEX);
+          Serial.print("\n");
+        }
+        if(flag && bt_flag)
+        {
+          Serial.println("button");
+          bt_flag = 0;
+        }
+      }
+   ```
+   ```
+        while(1)
+        {
+          Serial.println(myEncoder.getValue());
+          delay(100);
+          bt_flag = 1;
+        }
+   ```
+
+   3. Initialize the Encoder.The parameters are the SIGA pin and the callback function name, respectively.
+   
+   ```
+      GroveEncoder myEncoder(2, &myCallback);
+   ```
+