Add note about installation time

Author: sandeepmistry

README.md

@@ -40,6 +40,8 @@ Does not require a custom bootloader on the device.
  5. Open the Boards Manager from the Tools -> Board menu and install "Nordic Semiconductor nRF5 Boards"
  6. Select your nRF5 board from the Tools -> Board menu
 
+__NOTE:__ During installation it takes the Arduino IDE a few minutes to extract the tools after they have been downloaded, please be patient.
+
 #### OS Specific Setup
 
 ##### OS X