Add semaphore badge to README
Add semaphore badge to README

Adds the Semaphore badge to README (now that Semaphore is stable enough
that it's not erroring out all the time).

kadel/kedge,surajnarwade/kedge,surajnarwade/kedge,kedgeproject/kedge,kedgeproject/kedge,cdrage/kedge,cdrage/kedge,surajnarwade/kedge,kadel/kedge,ashetty1/kedge,kedgeproject/kedge,ashetty1/kedge,cdrage/kedge