docs(cli): add link to --extends usage (#7391)

Author: snitin315

src/content/api/cli.mdx

@@ -552,6 +552,8 @@ You can extend existing webpack configurations with the help of `--extends`:
 npx webpack --extends ./base.webpack.config.js
 ```
 
+Read more about it in [extending configurations](/configuration/extending-configurations/).
+
 ### json
 
 **Print result of webpack as JSON**