minor improvements for chat example

The chat example is obviously not meant to be a fully polished app, but still there may be some small UI improvements we could make:

Maybe text should come up from the bottom?
On mobile, rubber band vertical scrolling should only affect the inner message log area and not the whole screen.
Display the user's own username somewhere.
Display some "enter message:"-style prompt at the bottom or alternative visual, so it's obvious where to type.
Add a link to the code.

fanout / django-eventstream