docs: add codeclimate badge

README.md

@@ -39,6 +39,7 @@ At the time of badgen.now.sh's reveal, it had only four live badges as demonstra
 
 [![StandardJS][standard-src]][standard-href]
 [![Dependencies][dependencies-src]][dependencies-href]
+[![Maintainability][maintainability-src]][maintainability-href]
 
 We are using [StandardJS][standard-href] style, make sure you have ESLint/Standard plugin on your editor and have autofix enabled.
 
@@ -89,4 +90,6 @@ built with ⚡️ from [badgen](https://github.com/amio/badgen).
 [standard-src]: https://badgen.net/badge/code%20style/standard/pink
 [standard-href]: https://standardjs.com
 [deploy-to-now-src]: https://badgen.net/badge/▲/$%20now%20amio%2Fbadgen-service/333
+[maintainability-src]: https://badgen.net/codeclimate/maintainability/amio/badgen-service
+[maintainability-href]: https://codeclimate.com/github/amio/badgen-service
 [now-href]: https://zeit.co/now