Navigate to our forum for discussions (#1978)

* Navigate to our forum for discussions

* Update forum message

* Update config.yml

Author: fehiepsi

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,4 @@
+contact_links:
+  - name: Pyro Discussion Forum
+    url: https://forum.pyro.ai/
+    about: For general questions about NumPyro, please use the forum instead of GitHub issues.