Project: Adds support resource docs (#17699)

Adds a support resource document. For reference, 
https://help.github.com/en/articles/adding-support-resources-to-your-project.

Closes #17650

SUPPORT.md

+Need help or support?
+------------------
+
+ **Please note:**
+- Only submit issues for bug reports, feature requests or enhancements.
+- Grafana project uses GitHub mainly for tracking bugs and feature requests.
+- Asking a question by opening an issue will directly result in issue being closed.
+
+If you require help or support then ask a question and/or find existing questions/answers in the [Grafana community site](https://community.grafana.com/).
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