doc fixes for mcu 4
doc fixes for mcu 4

ivankravets/blynk-library,ivankravets/blynk-library,blynkkk/blynk-library,blynkkk/blynk-library,ivankravets/blynk-library,ivankravets/blynk-library,blynkkk/blynk-library,ivankravets/blynk-library,blynkkk/blynk-library,blynkkk/blynk-library