docs: remove the additional arg from documentation

Author: Aljoscha Gerber

docs/pre-commit-hooks.md

@@ -85,8 +85,8 @@ hooks:
 
 ## poetry-install
 
-The `poetry-install` hook calls the `poetry install --sync` command
-to make sure the installed dependencies match the packages defined in `poetry.lock`.
+The `poetry-install` hook calls the `poetry install` command
+to make sure all locked packages are installed.
 In order to install this hook, you either need to specify `default_install_hook_types`, or you have
 to install it via `pre-commit install --install-hooks -t post-checkout -t post-merge`.