updated broken link

Author: mcmchris

content/retired/04.other/hardware-pictures/content.md

@@ -55,7 +55,7 @@ Serial Single Sided - This board is designed to be etched and assembled by hand.
 
 ## Looking for an older board?
 
-The [hardware index](content/retired/04.other/arduino-older-boards) lists all the Arduino boards made and the differences between them.
+The [hardware index](https://docs.arduino.cc/retired/other/arduino-older-boards/) lists all the Arduino boards made and the differences between them.
 
 ## Shields