chore(docs): Add hf_hide_admin_menu to README (#17)

Author: ouun

README.md

@@ -83,6 +83,14 @@ Outside of defining your error messages on the options page, you can optionally
 />
 ```
 
+### Prevent moving Dashboard menu item
+
+By default the HTML Forms menu items is moved to the Options submenu. Prevent that by using the `hf_hide_admin_menu` hook:
+
+```php
+add_filter('hf_hide_admin_menu', '__return_false');
+```
+
 ## Bug Reports
 
 If you discover a bug in Sage HTML Forms, please [open an issue](https://github.com/log1x/sage-html-forms/issues).