Add documentation about option

README.md

@@ -339,5 +339,22 @@ ENV['ember-component-css'] = {
 }
 ```
 
+**patchClassicComponent**
+
+Set this option to `false` to prevent automatic `Component.reopen()` call which injects
+the autogenerated class into component's `classNames` property.
+
+You would need to use {{this.styleNamespace}} in *all* of your templates instead:
+
+```hbs
+<div class="wrapper {{this.styleNamespace}}">
+  Content goes here.
+</div>
+```
+
+This is required to use `ember-component-css` with Ember 4+ since `Component.reopen()` was removed from Ember.js codebase.
+For more details you may refer to [deprecation page](https://deprecations.emberjs.com/v3.x#toc_ember-component-reopen).
+
+
 ### [The announcement from EmberConf 2015](https://youtu.be/T1zxaEKeq3E)
 [![CSS is hard - EmberConf 2015](http://f.cl.ly/items/1a3a3r1C1y0D060D3j3u/EmberConf%202015%20-%20CSS%20Is%20Hard%20-%20YouTube%202015-03-22%2018-33-41.jpg)](https://youtu.be/T1zxaEKeq3E)