Expand the online forums list

[benmarwick]

• includes items from https://github.com/sje30/sharing-report/issues/10 and https://github.com/sje30/sharing-report/issues/3
• also incorporated most of @hanke's TODO's with citations or sentences, I hope they're ok
• edited a few other sentences here and there.
• added request to editor for text boxes, which hopefully will catch the reader's eye more than a few columns of text...

[benmarwick]

Sorry, the TODOs came from @yarikoptic in https://github.com/sje30/sharing-report/commit/d0961d88f10bb07c4a711871c3049f8f09828795, not @hanke, my mistake!