README.md: Add build status badges
README.md: Add build status badges

Add status badges for Travis CI, AppVeyor CI and Code coverage
for codecov.io

NIT-dgp/UIP,Aniq55/UIP,VK10/UIP,NIT-dgp/UIP,nemaniarjun/UIP,nemaniarjun/UIP,Aniq55/UIP,VK10/UIP