You can find a repository with examples here
There is a tutorials section in this documentation.
This site is hosted at github and has its own github repository, so you can fork it, and make a PR :)
https://github.com/jtransc/jtransc/tree/master/docs
Also, pressing the pencil button available in each page, you can see the corresponding file on github. And github will provide another pencil button which will create a fork in your user so you can edit the file and do a PR.
You can read the complete information about contributing.