Hi Abigail,
But to answer your question, you can find the documentation for previous versions in the /docs subfolder of your jsPsych download. That subfolder contains all of the markdown-formatted documentation files that would've appeared on the website along with that particular release. And if you don't have that subfolder anymore, you can always go back through the old jsPsych releases and view or download the files again.
Cheers,
Becky