Improvements to "Reporting RabbitMQ Issues" and support docs

[lukebakken]

https://github.com/rabbitmq/support-tools/blob/master/docs/Reporting_RabbitMQ_Issues.md

• Does this document live in the "correct" place? Should it be part of the website?
• Should there be recommendations for getting support, i.e -
  • monitoring is required
  • log history is required
• Each bullet point in the "reporting issues" could give a rationale for the information, and tips for collecting it.
• A document or flow-chart with how to diagnose issues could be added (runbooks)