Update issue templates (#3282)

.github/ISSUE_TEMPLATE/config.yml

 blank_issues_enabled: false
+contact_links:
+  - name: ML-Agents Unity Forum
+    url: https://forum.unity.com/forums/ml-agents.453/
+    about: Please ask Installation / Setup and Discussion / General Questions in the Unity Forum.

.github/ISSUE_TEMPLATE/discussion---general-questions.md

 
 ---
 
-Describe what you'd like to discuss.
+For discussions, please post in [ML-Agents Unity Forum](https://forum.unity.com/forums/ml-agents.453/) instead of
+creating a Github issue. Unity forums are the predominant community for Unity users and experts. By leveraging Unity
+forums for general discussions and project help, we can keep Github issues for bugs, performance issues, and feature
+requests for ML-Agents.
+
-**Note**: The ML-Agents team has limited resources for education and community discussion.  We'll participate as we are able, but encourage members of the community to support one another to discuss and support one another.
+**Note**: The ML-Agents team has limited resources for education and community discussion.  We'll participate as we are
+able, but encourage members of the community to support one another to discuss and support one another.

.github/ISSUE_TEMPLATE/discussion---installation-and-setup.md

+---
+name: Installation / Setup
+about: Questions about python installation, initial connection between Unity and training, etc.
+title: ''
+labels: installation
+assignees: ''
+
+---
+
+For installation and initial setup questions, please post in [ML-Agents Unity Forum](https://forum.unity.com/forums/ml-agents.453/)
+instead of creating a Github issue. Include steps to reproduce, error logs, and any other relevant information about
+your versions and platform.