Update README.md

README.md

@@ -65,4 +65,5 @@ composer composerize-drupal --composer-root=. --drupal-root=.
 * `--composer-root`: Specifies the root directory of your project where `composer.json` will be generated. This should be the root of your Git repository, where `.git` is located.
 * `--drupal-root`: Specifies the Drupal root directory where `index.php` is located.
 * `--no-update`: Prevents `composer update` from being automatically run after `composer.json` is generated.
+* `--no-gitignore`: Prevents modification of the root .gitignore file. 
 * `--exact-versions`: Will cause Drupal core and contributed projects (modules, themes, profiles) to be be required with exact verions constraints in `composer.json`, rather than using the default caret operator. E.g., a `drupal/core` would be required as `8.4.4` rather than `^8.4.4`. This prevents projects from being updated. It is not recommended as a long-term solution, but may help you convert to using Composer more easily by reducing the size of the change to your project.