close #290 cleanup command fails for multiple delivered branches

Author: groenborg

docs/documentation.md

@@ -199,6 +199,8 @@ git phlow cleanup
 cleanup is for tidying up the git workspace. As you follow the workflow a lot of branches prefixed with `delivered/` will be in the workspace, and should just be deleted if they have been successfully integrated. Running the command will remove these branches locally and remote as well. A local version of this command is available, and will just remove the local branches.
 Some branches can not be deleted, because git cannot detect if they have been integrated into the integration branch. That can be due to a rebase or squash. Those can be deleted with the `force` flag. 
 
+git cannot always detect if a branch have been integrated,so for those you have to run delete with `--force`
+
 ### config
 ```
 git phlow config