Update README.md

Author: khoih-prog

README.md

@@ -55,12 +55,12 @@ How to use:
 #include "ESP8266TimerInterrupt.h"
 
 #ifndef LED_BUILTIN
-#define LED_BUILTIN       2         // Pin D2 mapped to pin GPIO2/ADC12 of ESP32, control on-board LED
+#define LED_BUILTIN       2         // Pin D4 mapped to pin GPIO2/TXD1 of ESP8266, NodeMCU and WeMoS, control on-board LED
 #endif
 
 volatile uint32_t lastMillis = 0;
 
-void IRAM_ATTR TimerHandler(void)
+void ICACHE_RAM_ATTR TimerHandler(void)
 {
   static bool toggle = false;
   static bool started = false;