* guix/scripts/import.scm (show-help): Add newline before a list of
importers.
* guix/scripts/lint.scm (show-help): Split a long description line.
* guix/scripts/package.scm (show-help): Improve docstrings for --install
and --remove options.
* guix/scripts/system.scm (show-help): Format actions the same way as
guix commands and importers are formatted.