Add "CAN" modal.

Hardware-API.md

@@ -12,8 +12,9 @@ The existing `pyb` module already provides such abstraction but it is not as cle
 # Terminology
 
 * Port - when used in this document, refers to some kind of hardware port.
-* Software - MicroPython ported to a particular CPU/MCU/SoC. A separate word used to disambiguate word "port" (which otherwise may refer to a hardware or software port)
+* Software - MicroPython as a project, and particular implementation ported to a particular CPU/MCU/SoC. A separate word used to disambiguate word "port" (which otherwise may refer to a hardware or software port)
 * MUST, SHOULD, MAY - Have meanings based on https://www.ietf.org/rfc/rfc2119.txt
+* CAN - Gives an example how feature with undefined behavior may act on a particular software implementation. Essentially, it's a note for implementers, from API side, the behavior stays undefined.
 
 # Use cases