JSFiddle doesn't support IE (even 11) anymore so we shouldn't advise users
to use it to create test cases. To make people have a choice, add CodePen
to the list.
Also, link to specific starter templates so that novices don't need to spend
time thinking how to set up the basic structure.
Closes gh-4289
We no longer support jQuery 1.x/2.x and mentioning 3.x would just mean the text
gets out of date once we release jQuery 4. We only really support the latest
jQuery version so let's make that clear.
Closes gh-3372
