docs: Add references

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

Author: brlin-tw

README.md

@@ -4,6 +4,13 @@ This project provides a common base of Markdownlint(Node.js variant)'s configura
 
 [![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)
 
+## Reference
+
+* [igorshubovych/markdownlint-cli: MarkdownLint Command Line Interface](https://github.com/igorshubovych/markdownlint-cli#configuration)  
+  Official project site
+* [markdownlint/Rules.md at main · DavidAnson/markdownlint](https://github.com/DavidAnson/markdownlint/blob/main/doc/Rules.md)  
+  Description of the official linting rules
+
 ## License
 
 Unless otherwise specified, this product is released with [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.