Add CircleCI example

[ianfixes]

Feature Request

Add CircleCI to this project and report its status in the README

Example Code

.circleci/config.yml via @TomohiroHayashi

version: 2
jobs:
  build:
    machine: true    
    steps:
      - checkout

      - run:
          name: install and execute
          command: |
            bundle install
            bundle exec arduino_ci_remote.rb

Example README.md section

Platform	Travis CI	AppVeyor	CircleCI
OSX			NEW BADGE HERE
Linux			NEW BADGE HERE
Windows

[ianfixes]

Example is here Arduino-CI/Blink#1