Merge branch 'ks/prepare-commit-msg-sample'

Remove an example that is now obsolete from a sample hook,
and improve an old example in it that added a sign-off manually
to use the interpret-trailers command.

* ks/prepare-commit-msg-sample:
  hook: add a simple first example
  hook: add sign-off using "interpret-trailers"
  hook: name the positional variables
  hook: cleanup script