ci: Add cirrus configuration

Author: laanwj

.cirrus.yml

@@ -0,0 +1,19 @@
+container:
+  image: ruby:2.5.5
+
+task:
+  name: website
+  env:
+    JEKYLL_ENV: production
+    NOKOGIRI_USE_SYSTEM_LIBRARIES: true # speeds up installation of html-proofer 
+    RUBYOPT: "-KU -E utf-8:utf-8"
+
+  bootstrap_script: gem install bundler
+  bundler_cache:
+    folder: /usr/local/bundle
+    fingerprint_script:
+      - echo $RUBY_VERSION
+      - cat Gemfile.lock
+    populate_script: bundle install
+
+  build_and_test_script: make all