Add documentation for how to create a JSBin

[maxkfranz]

Description of new feature

What should the new feature do? For visual features, include an image/mockup of the expected output.

Add documentation so it's easier for people to post a JSBin demo. JSBin is preferred since it only requires a Github account, which you must have when posting an issue anyway.

This could be in steps in the issue template:

1. Go to our base JSBin: http://jsbin.com/fiqugiq
2. Click the 'Edit in JSBin' button in the top-right corner.
3. Click File > Clone to make your own copy of the demo (with its own unique URL) that you can edit.
4. Edit the JSBin to reproduce your issue.
5. Post the link to your JSBin here.

We could also include a video of the steps, but the steps seem pretty clear to me.

Motivation for new feature

Describe your use case for this new feature.

A fair number of people have trouble posting a JSBin, and so they don't post a reproducible demo that we can use to verify the bug and debug it.

For reviewers

Reviewers should ensure that the following tasks are carried out for incorporated issues:

• Ensure that the reporter has adequately described their idea. If not, elicit more information about the use case. You should iteratively build a spec together.
• Ensure that the issue is a good fit for the core library. Some things are best done in extensions (e.g. UI-related features that aren't style-related). Some things are best done by app authors themselves -- instead of in Cytoscape libraries.
• The issue has been associated with a corresponding milestone.
• The commits have been incorporated into the unstable branch via pull request. The corresponding pull request is cross-referenced.

[maxkfranz]

@mikekucera

What do you think, Mike?

[mikekucera]

Sounds good.

I'm also happy if a user attaches a single-page html file with embedded scripts that can reproduce the issue. With copilot its very easy to ask it to create an html file with a cytoscape.js canvas as a starting point.

[maxkfranz]

I agree that the single-page html files are pretty good. I've found the JSBins more productive in the past since:

1. When people upload html files they tend to include large portions of their app. I'm not sure why, but they don't tend to do this for JSBins.
2. It's much easier to quickly verify if there is a bug or not.

How about keeping the instructions as JSBin-only, but then we manually ask users for an html file upload if they can't manage the JSBin?