Consider where Board of Directors Handbook should go

[maneesha]

There is a Board of Directors Handbook. We have not yet included it on this site because BoD is different from other community roles. Opening this issue to consider where we want to keep this document.

For reference, on a related note, The Carpentries Bylaws used to be in the Handbook. With the change in our governance, the Bylaws are no longer in the Handbook and are now in a PDF linked from the governance page of the new website.