improvements on registration form

A feedback that we had from new users on our instance is that they find the registration form a bit confusing. Mainly the "Bio" was what they didn't really understand. I propose three changes

1. Make it clear that Bio is optional (the rest isn't)
2. Change from input to textarea. A Bio typically has newlines, a textarea is better for that
3. Add an example-Bio similar to how we do for Username and Display Name

I played around in the DOM a bit and made a mockup

I also noticed that the translations don't seem to work for the examples. It would be nice if those could be translated as well.

How it is now:

How it could be:

What I did: