Tutorial for Widget TextEditor

[lycheeje11y]

I think that this one in particular would be a very useful tutorial. It took me a lot of pain to figure out how to get started with the TextEditor widget. I would open a pull request, but I have only just begun to get familiar with it...once I learn it completely I can open a PR. I'm not at that point yet, though. So I thought I'd open an issue and see if it gains any traction. Maybe I'll be able to open a PR by the end of this week. Would adding a chapter for the TextEditor widget be acceptable?

[fogarecious]

Yes, welcome to add new materials. Basically, the tutorial is kept as simple as possible, so take it easy. Let me know if you need any help. Feel free to make a pull request and take your time.