Explain how to run reference benchmark on a dev branch

Create a short document to:

• Explain the flow of tasks and resources used by the reference benchmark job https://qa.nuxeo.org/jenkins/job/Misc/job/nuxeo-reference-bench/
  listing CI jobs, git repository, web site, and s3 buckets
• Explain the build parameters
• Give some convention recommendation
• Explain how to add "Analysis" documentation on a bench suite

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Doc updated on nuxeo-bench repository See https://github.com/nuxeo/nuxeo-bench#misc-benchmark for the custom usage.