docs(README): remove broken badges and links

README.md

@@ -8,7 +8,6 @@
 [![Documentation Status](https://readthedocs.org/projects/portainer/badge/?version=stable)](http://portainer.readthedocs.io/en/stable/?badge=stable)
 [![Build Status](https://semaphoreci.com/api/v1/portainer/portainer-ci/branches/develop/badge.svg)](https://semaphoreci.com/portainer/portainer-ci)
 [![Code Climate](https://codeclimate.com/github/portainer/portainer/badges/gpa.svg)](https://codeclimate.com/github/portainer/portainer)
-[![Slack](https://portainer.io/slack/badge.svg)](https://portainer.io/slack/)
 [![Gitter](https://badges.gitter.im/portainer/Lobby.svg)](https://gitter.im/portainer/Lobby?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge)
 [![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg)](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=YHXZJQNJQ36H6)
 
@@ -20,8 +19,6 @@
 
 ## Demo
 
-<img src="https://portainer.io/images/screenshots/portainer.gif" width="77%"/>
-
 You can try out the public demo instance: http://demo.portainer.io/ (login with the username **admin** and the password **tryportainer**).
 
 Please note that the public demo cluster is **reset every 15min**.