meta: add ISSUE_TEMPLATE config.yml

For now, it only adds a link to the Discord server.

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,5 @@
+blank_issues_enabled: true
+contact_links:
+  - name: Get help on Discord
+    url: https://discord.gg/ohmyzsh
+    about: Have a quick question? Join the Discord server and ask on the appropriate channel.