Update GitHub template to steer feature requests to community forum

Thanks to @EwoutH for doing this on Signal-iOS and Signal-Android!

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,20 @@
+blank_issues_enabled: false
+contact_links:
+  - name: ✨ Feature request
+    url: https://community.signalusers.org/c/feature-requests/
+    about: Missing something in Signal? Let us know.
+  - name: 📚 Translation feedback
+    url: https://community.signalusers.org/c/translation-feedback/
+    about: Share feedback on translations
+  - name: 📃 User documentation
+    url: https://support.signal.org/
+    about: Search for any questions you have about Signal
+  - name: 💬 Community support
+    url: https://community.signalusers.org/c/support/
+    about: Feel free to ask anything
+  - name: 📖 Contribution instructions
+    url: https://github.com/signalapp/Signal-Desktop/blob/development/CONTRIBUTING.md
+    about: Want to contribute to Signal Desktop? Start here.
+  - name: ❓ Other issue?
+    url: https://community.signalusers.org/
+    about: Search on the community forums