Update labels and alt text, add link to hardware reference

Development_Environment/Boards/imx8.rst

@@ -55,16 +55,19 @@ time of writing (2018-12-09), so an external display is highly recommended.
 
 .. figure:: images/dev-board-sockets-buttons-switches.png
    :scale: 50%
-   :alt: Port side, in order: 4-pole 3.5mm CTIA audio socket, RJ45 Ethernet
+   :alt: Port side, in order: 3.5mm audio socket, RJ45 Ethernet
          socket, mini HDMI socket, USB C socket, micro SD card socket.
          Kill switch side, in order: reset button, boot mode switch, camera
-         kill switch, cellular kill switch, Wi-Fi kill switch.
+         + microphone kill switch, cellular kill switch, Wi-Fi kill switch.
          Button side, in order: smart card socket, volume down button, volume
          up button, power button, micro SIM card socket.
 
    The positions and types of sockets, push buttons and switches (click
    to enlarge)
 
+See :ref:`hardware_reference` for information about the specific parts used
+for the sockets, buttons and switches.
+
 .. _devkit_test_run:
 
 Test Run