message: Add Danfoss wiring page link to CAN guide
diff: @@ -10,8 +10,12 @@ Borrowing from [Wikipeda](https://en.wikipedia.org/wiki/CAN_bus):
  In simple terms, CAN is a way of communicating between many devices over a single twisted pair of wires. The signal is transmitted as the difference in voltage between the two wires (differential signalling), which makes it very robust against noise. Instead of using a unique address (like I2C) or a select pin (like SPI), CAN *messages* have a unique ID that also acts as the priority. At the beginning of a message frame, all devices talk and read at the same time. As the message ID is transmitted, the lowest value "wins" and that message will be transmitted (ID **0** has the *highest* priority). All other devices will wait for the next chance to send. If two devices send the same message ID at the same time, they will conflict and a bus failure may occur. Make sure your devices can never send the same message ID at the same time!
  +See also this great article from Danfoss that quickly describes how to put together the wiring for a CAN bus https://danfosseditron.zendesk.com/hc/en-gb/articles/360042232992-CAN-bus-physical-layer
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  ![CAN picture](screenshots/CAN_Bus_Drawing.png)
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  ## Why use CAN?
  CAN is convenient for its simple and robust Physical Layer (PHY) that requires only a twisted pair of wires and a 120ohm termination resistor at each end. It has low jitter and low latency, because there is no host computer. It is relatively fast (CAN 2.0b supports 1 Mbps). Messages are easy to configure and load with data. Transceivers and controllers are inexpensive and widely available, thanks to its use in automotive.
  