README: Add coverage badge
README: Add coverage badge

Not too good at the moment, but we're getting there...

Signed-off-by: Samuel Ortiz <0ba86cb3f08bbb861958e54bd3438887adb4263c@linux.intel.com>

ciao-project/ciao,ciao-project/ciao,tpepper/ciao,kaccardi/ciao,wcwxyz/ciao,mcastelino/ciao,jorgevgut/ciao,leoswaldo/ciao,erick0z/ciao,matthewrsj/ciao,obedmr/ciao,chavafg/ciao,mrkz/ciao,markdryan/ciao,01org/ciao,wcwxyz/ciao,leoswaldo/ciao,mrkz/ciao,tpepper/ciao,jorgevgut/ciao,kaccardi/ciao,wcwxyz/ciao,leoswaldo/ciao,markdryan/ciao,erick0z/ciao,erick0z/ciao,chavafg/ciao,rbradford/ciao,tpepper/ciao,matthewrsj/ciao,mrkz/ciao,rbradford/ciao,obedmr/ciao,matthewrsj/ciao,obedmr/ciao,mcastelino/ciao,mcastelino/ciao,01org/ciao,jorgevgut/ciao