Preview Pull For Mining Guide

Created this to help keep track of work being done before the pull request against the main bitcoin.org repository.  Feedback both here and on the mailing list is welcome.

**Warning:** the commits shown on this pull will be squashed down to one commit per author for the real pull.
Good idea, but when I tried it, Iceweasel (FF) versions 17 & 24 won't let me copy the text in the disabled boxes.  Chromium 28 & 34 do let me copy, but I think it might be best to not use disabled for the FF users.