Log rotate patch

- Add install hook, that create sudoers cfg for running "lib/dokku-cfg-logrotate" command which update /etc/logrotate.d/dokku-app.d/$APP rotate cfg (logrotate require these cfg be as root owner and 644).
- Update Readme for installing and logrotate
- Fix progrium/buildstep, supervisor command now /exec_svd, which is copy of /exec generated by "builder".
- Some indent of echo