update README with Appveyor badge

related to #1881

README.md

@@ -21,8 +21,9 @@ or CSS3 selectors.
 ## Status
 
 [![Concourse CI](https://ci.nokogiri.org/api/v1/teams/nokogiri-core/pipelines/nokogiri/jobs/ruby-2.4-system/badge)](https://ci.nokogiri.org/teams/nokogiri-core/pipelines/nokogiri)
-[![Test Coverage](https://api.codeclimate.com/v1/badges/59c67b0e8976027a45ad/test_coverage)](https://codeclimate.com/github/sparklemotion/nokogiri/test_coverage)
+[![Appveyor CI](https://ci.appveyor.com/api/projects/status/xj2pqwvlxwuwgr06/branch/master?svg=true)](https://ci.appveyor.com/project/flavorjones/nokogiri/branch/master)
 [![Code Climate](https://codeclimate.com/github/sparklemotion/nokogiri.svg)](https://codeclimate.com/github/sparklemotion/nokogiri)
+[![Test Coverage](https://api.codeclimate.com/v1/badges/59c67b0e8976027a45ad/test_coverage)](https://codeclimate.com/github/sparklemotion/nokogiri/test_coverage)
 
 [![Gem Version](https://badge.fury.io/rb/nokogiri.svg)](https://rubygems.org/gems/nokogiri)
 [![SemVer compatibility](https://api.dependabot.com/badges/compatibility_score?dependency-name=nokogiri&package-manager=bundler&version-scheme=semver)](https://dependabot.com/compatibility-score.html?dependency-name=nokogiri&package-manager=bundler&version-scheme=semver)