docs: Add CI status badge

Signed-off-by: 林博仁(Buo-ren Lin) <Buo.Ren.Lin@gmail.com>

Author: brlin-tw

README.md

@@ -2,6 +2,8 @@
 
 This project provides a common base of Markdownlint(Node.js variant)'s configuration file(.markdownlint.yml) that should be easily adaptable for most project's with little modifications.
 
+[![The indication badge of Continuous Integration(CI)'s current status](https://cloud.drone.io/api/badges/Lin-Buo-Ren/common-markdownlint-configs-nodejs/status.svg "Continuous Integration(CI) status")](https://cloud.drone.io/Lin-Buo-Ren/common-markdownlint-configs-nodejs)
+
 ## License
 
 This template uses [the Creative Commons Attribution-ShareAlike License, version 4.0](https://creativecommons.org/licenses/by-sa/4.0), or any more recent version of your choice, with an exception of the license only covers the configuration file itself, but not other assets in your project.