Update README.md

Merges https://github.com/espressif/esp-idf/pull/3104

examples/peripherals/mcpwm/mcpwm_servo_control/README.md

@@ -6,11 +6,11 @@ Assign pulse width range and the maximum degree, accordingly the servo will move
  
 
 ## Step 1: Pin assignment
-* GPIO15 is assigned as the MCPWM signal for servo motor 
+* GPIO18 is assigned as the MCPWM signal for servo motor 
 
 
 ## Step 2: Connection
-* connect GPIO15 with servo pwm signal
+* connect GPIO18 with servo pwm signal
 * other two wires of servo motor are VCC and GND