Add GitHub issue templates

Add templates to point users towards the community support channels.

Signed-off-by: Ben Kochie <superq@gmail.com>

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,21 @@
+---
+name: Feature request
+about: Suggest an idea for this project.
+title: ''
+labels: ''
+assignees: ''
+---
+
+<!--
+
+    Please do *NOT* ask usage questions in Github issues.
+
+    If your issue is not a feature request or bug report use our community support.
+
+    https://prometheus.io/community/
+
+-->
+## Proposal
+**Use case. Why is this important?**
+
+*“Nice to have” is not a good use case. :)*