docs(extensions): improved cases when using always

Author: wenfangdu

Diff for: docs/rules/extensions.md

@@ -109,6 +109,8 @@ import foo from './foo';
 import bar from './bar';
 
 import Component from './Component';
+
+import foo from '@/foo';
 ```
 
 The following patterns are not considered problems when configuration set to "always":
@@ -121,6 +123,8 @@ import bar from './bar.json';
 import Component from './Component.jsx';
 
 import * as path from 'path';
+
+import foo from '@/foo.js';
 ```
 
 The following patterns are considered problems when configuration set to "ignorePackages":