Coverage for Canada

[jlevy]

This issue is to track writing of a supplement to the guide that lists everything specific/different in Canada. Follows on to #26.

This could be a single new section, or if it becomes excessively long, a new file.

In the short term, we won't change the US bias of the original file, but once this is written, it will be easier to tease out the common parts and separate out sections for each country.