v1.3.1 to add waitingForDRD() function

### Releases v1.3.1

1. Add waitingForDRD() function to signal in DRD wating period. Check [DRD is waiting for a double reset? #14](#14)
2. Add example [checkWaitingDRD](https://github.com/khoih-prog/ESP_DoubleResetDetector/tree/master/examples/checkWaitingDRD) to demo how to use the new feature.

Author: khoih-prog

examples/checkWaitingDRD/checkWaitingDRD.ino

@@ -17,7 +17,7 @@
 // For ESP8266, You must select one to be true (RTC, EEPROM, LITTLEFS or SPIFFS)
 // Otherwise, library will use default EEPROM storage
 
-// This example demonstrate how to use new function waitingForDRD() to signal the stage of DRD
+// This example demonstrates how to use new function waitingForDRD() to signal the stage of DRD
 // waitingForDRD() returns true if in DRD_TIMEOUT, false when out of DRD_TIMEOUT
 // In this example, LED_BUILTIN will blink in DRD_TIMEOUT period, ON when DR has been detected, OFF otherwise