Added information about license key.

.npm/README.md

@@ -21,7 +21,19 @@ With CKEditor 4 LTS, security updates and critical bug fixes are guaranteed unti
 
 After June 30, 2023 the `master` version of the [LICENSE.md](https://github.com/ckeditor/ckeditor4/blob/master/LICENSE.md) file changed to reflect the license of CKEditor 4 LTS available under the Extended Support Model.
 
-All future versions of CKEditor 4 are released as CKEditor 4 LTS distributions and require a license key.
+All future versions of CKEditor 4 (4.23.0-lts and above) are released as CKEditor 4 LTS distributions and require a license key.
+
+If you acquired the [Extended Support Model](https://ckeditor.com/ckeditor-4-support/) for CKEditor 4 LTS, please read [the CKEditor 4 LTS key activation guide.](https://ckeditor.com/docs/ckeditor4/latest/support/licensing/license-key-and-activation.html)
+
+In order to activate CKEditor 4 LTS, add `licenseKey` configure the editor with a valid license key:
+
+```html
+<script>
+    CKEDITOR.replace( 'editor', {
+        licenseKey: 'your license key'
+    } );
+</script>
+```
 
 The NPM package is tagged as 4.23.* without the `-lts` suffix, to keep it consistent with NPM versioning guidelines. Note that the version 4.23.0 and above are the LTS versions of the editor.