update README to notify about upcoming change to debhelper 7
update README to notify about upcoming change to debhelper 7

sathieu/stdeb,pombredanne/stdeb,pombredanne/stdeb,astraw/stdeb,benthomasson/stdeb,astraw/stdeb,LeMeteore/stdeb,benthomasson/stdeb,sathieu/stdeb,sathieu/stdeb,benthomasson/stdeb,LeMeteore/stdeb,astraw/stdeb,pombredanne/stdeb,LeMeteore/stdeb