[BENTO-111] Added a .gitattributes and a note in README about Windows hosts
 * A .gitattributes was added to the repository to ensure ks.cfg, preseed.cfg
   and *.sh files have correct LF line endings and *.bat files have
   correct CRLF line endings.
 * Added a note about this in the README so people packaging boxes
   from Windows Hosts can fix the problem if they encounter it.