Update Dexcom charge hint

The charging icon on the Dexcom cycling on and off is also a good indication it needs charging.

docs/docs/walkthrough/phase-2/using-openaps-tools.md

@@ -169,7 +169,7 @@ Go ahead and try some more pump uses to find out what they do. Note that some of
 
 Now let's try communicating with the Dexcom receiver.
 
-Hint: Your Dexcom should be nearly fully charged before plugging it in to your Raspberry Pi. If, when you plug in your Dexcom, it causes your WiFi dongle to stop blinking, that is a sign that it is drawing too much power and needs to be charged. 
+Hint: Your Dexcom should be nearly fully charged before plugging it in to your Raspberry Pi. If, when you plug in your Dexcom, it causes your WiFi dongle to stop blinking, or if the charging icon on the Dexcom keeps cycling on and off, that is a sign that it is drawing too much power and needs to be charged. 
 
 > Workaround: If you continue to have problems, try increasing the mA output to the USB ports, you can do this by running the following command `$ sudo bash -c "echo -e \"#Enable Max USB power\nmax_usb_current=1\" >> /boot/config.txt"`.