Please share your attempts! :)

The manual is not the best place to look for examples.  Instead, you'd
be best off looking at similar package declarations among the
distribution's official packages.  `guix` even provides a shortcut for
this, for instance:

  $ guix edit xfce4-battery-plugin



Off-topic:  I'm an mu4e user and for the past few e-mails Jone has sent,
they were all time-stamped from about 2 hours ahead in the future.
At UTC+1, I'm writing this at 17:27 while Jone's e-mail is timestamped
at 19:34.

Jone, would you have any clue why that is?  Anyone?

--
Pierre Neidhardt