IMPORTANT: guix-package -> guix package

[Mark H Weaver]

Hello all,

In git, the five scripts 'guix-package', 'guix-gc', 'guix-build',
'guix-download' and 'guix-import' have been replaced with the single
script 'guix'.  The new usage replaces 'guix-package' with 'guix
package', and more generally 'guix-COMMAND' with 'guix COMMAND'.

After pulling, please delete the old scripts from your build directory
to avoid running them by mistake.  Please delete them from ${prefix}/bin
after "make install" as well.

    Thanks,
      Mark