Slack image and updated README with better link. (#2473)

* Added Slack link to README.

* Updated Slack link and added image.

* Update README.md

* Add files via upload

* Update README.md

* Delete slack.svg

README.md

@@ -3,6 +3,7 @@ chromebrew
 
 Package manager for Chrome OS
 
+<a href="https://join.slack.com/t/chromebrew/shared_invite/enQtNDA2MTQ5ODQ3NDc2LTA0ZmJlMGFmNmZhOTYwNDE3ZDY0NDA0MWI0OTE3MzJkYTQxN2UxMWQ1YTEzOWFmNTliMGM4NDZjYzY2NjczZGE" target="_blank"><img src="/images/slack.jpg" alt="Slack Invite" /></a>
 [Join the chat on Slack](https://join.slack.com/t/chromebrew/shared_invite/enQtMzUzMjI3NzU2NzUzLWViMGMzNzY1MDk0YTI5Y2RkMTIxMTY3OGQ0ZDYzMDRjODE0ZWI2NTM5MjBkM2Q4NGNlYzY4MGM1MzM2ZTI4NTQ)
 
 Supported Systems