add api scope to docs

Author: kriskbx

documentation.md

@@ -44,7 +44,7 @@ gtt config
 ```
 
 Add your GitLab API url and your [GitLab API personal token](https://gitlab.com/profile/personal_access_tokens) 
-to the config file and save it afterwards:
+to the config file and save it afterwards. **You need to activate the `api` scope when creating your access token.**
 
 ```yaml
 url: https://gitlab.com/api/v4/