Merge pull request #3716 from yichengq/add-sem-badge

README: add semaphore CI status badge into README

README.md

@@ -1,6 +1,7 @@
 # etcd
 
 [![Build Status](https://travis-ci.org/coreos/etcd.svg?branch=master)](https://travis-ci.org/coreos/etcd)
+[![Build Status](https://semaphoreci.com/api/v1/projects/406f9909-2f4f-4839-b59e-95082cb088f1/575109/badge.svg)](https://semaphoreci.com/coreos/etcd)
 [![Docker Repository on Quay.io](https://quay.io/repository/coreos/etcd-git/status "Docker Repository on Quay.io")](https://quay.io/repository/coreos/etcd-git)
 
 **Note**: `master` branch may be in *unstable or even broken state* during development. Please use [releases][github-release] instead of `master` branch to get stable binaries.