Add "user support" contributor page

[SoryRawyer]

We currently link directly to the "support and helpdesk" section of the forum from this box on the community page. There are two things I think we could do with a dedicated documentation page:

1. Provide a brief orientation to providing user support for OpenRefine: how do people usually ask questions? what are the expectations for conduct on the forum?
2. Expand this contributor role to include contributions like testing and issue triage. Providing user support requires skills that overlap with these contribution types and it would provide more ways to engage with the project.