Added info on the community Powershell slack team (PowerShell#2062)

* Added info on the community Powershell slack team

* Revised update about Slack team to readme.md

* remove unneeded where

* Adds a line break before the gitter badge

* added missing full stops (periods)

Author: kilasuit

README.md

@@ -52,8 +52,13 @@ Chat Room
 
 Want to chat with other members of the PowerShell community?
 
+We have a Gitter Room which you can join below.
+
 [![Join the chat at https://gitter.im/PowerShell/PowerShell](https://badges.gitter.im/PowerShell/PowerShell.svg)](https://gitter.im/PowerShell/PowerShell?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 
+There is also the community driven PowerShell Slack Team which you can sign up for at [Slack Signup]. 
+
+[Slack Signup]: http://slack.poshcode.org
 Building the Repository
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