Update README.md

Removed "Introduction to Ember FastBoot" video that is no longer available on Vimeo.
Updated reference of "Ember community slack" to "Ember Community Discord".

Author: jad359

README.md

@@ -16,10 +16,6 @@ Limitations](#known-limitations) below for a full-list.
 The bottom line is that you should not (yet) expect to install this add-on in
 your production app and have FastBoot work.
 
-## Introduction Video
-
-[![Introduction to Ember FastBoot](https://i.vimeocdn.com/video/559399270_640x360.jpg)](https://vimeo.com/157688134)
-
 ## Installation
 
 FastBoot requires Ember 2.3 or higher. It is also preferable that your app is running `ember-cli` 2.12.0 and higher.
@@ -733,4 +729,4 @@ DEBUG=fastboot-test npm test
 
 ### Questions
 
-Reach out to us in Ember community slack in the `#-fastboot` channel.
+Reach out to us via [Ember Community Discord](https://discordapp.com/invite/zT3asNS) in the `#fastboot` channel.