The current way to define a news entry in Home-Manager is error prone
(since you need to type the date manually) and also it is common cause
of conflicts after merges because all entries are defined in the same
file.
This commit fixes this: we can now create individual news entries for
each new entry. A script `create-news-entry.sh` also helps to create it
in the correct format (with the correct filenames and structure).
