README: Add coveralls.io badge
README: Add coveralls.io badge

stuertz/restic,middelink/restic,jayme-github/restic,jayme-github/restic,howeyc/restic,bchapuis/restic,restic/restic,arithmetric/restic,kurin/restic,ar-jan/restic,kurin/restic,pombredanne/restic,middelink/restic,episource/restic,mappu/restic,fawick/restic,klauspost/restic,ar-jan/restic,stuertz/restic,byo/restic,intfrr/restic,byo/restic,fawick/restic,restic/restic,ckemper67/restic