Update kill switch and audio labels, fix alt text

Development_Environment/Boards/imx8.rst

@@ -55,7 +55,12 @@ time of writing (2018-12-09), so an external display is highly recommended.
 
 .. figure:: images/dev-board-sockets-buttons-switches.png
    :scale: 50%
-   :alt: The positions and types of sockets, push buttons and switches
+   :alt: Port side, in order: 4-pole 3.5mm CTIA 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.
+         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)