Newline in event.st necessary for proper behaviour

`yst create mysite` creates, among other things, `event.st`. Deleting the newlines at the end of this file causes the items to be all squished into one item. I guess this has something to do with moving to a new line for the new item. But this new line is important and perhaps the `README` should mention it.

Start by reproducing `yst create mysite` and inspect the generated `event.st` file, then read the README sections describing generated files or templates. Done means the importance of the trailing newlines is clearly documented, with the behavior of deleting them explained.

Written by the indexing model from the issue text.