Add links to slack + book when creating an issue. Add link to Slack at the top of the main README. (#482)

Author: spier

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,8 @@
+blank_issues_enabled: true
+contact_links:
+  - name: Slack
+    url: https://innersourcecommons-inviter.herokuapp.com
+    about: Join our Community on Slack for help and a casual chat.
+  - name: Patterns Book
+    url: https://patterns.innersourcecommons.org
+    about: Read our most mature patterns here.

README.md

@@ -1,5 +1,6 @@
 [![Check Links](https://github.com/InnerSourceCommons/InnerSourcePatterns/actions/workflows/link-checker.yml/badge.svg)](https://github.com/InnerSourceCommons/InnerSourcePatterns/actions/workflows/link-checker.yml)
 [![Pattern Syntax Validation](https://github.com/InnerSourceCommons/InnerSourcePatterns/actions/workflows/lint-patterns.yml/badge.svg)](https://github.com/InnerSourceCommons/InnerSourcePatterns/actions/workflows/lint-patterns.yml)
+[![Join our Slack!](https://img.shields.io/static/v1?message=join%20chat&color=9cf&logo=slack&label=slack)](https://innersourcecommons-inviter.herokuapp.com)
 
 # InnerSource Patterns