makechrootpkg: clarify usage message

    echo ""

    echo "The chroot shell 'root' directory must be created via the following"

    echo "command:"

    echo "    mkarchroot \$CHROOT_SHELL base base-devel sudo"

    echo "    mkarchroot \$CHROOT_SHELL/root base base-devel sudo"

    echo ""

    echo "If you have problems passing params to makepkg or need to pass long"

    echo "options, put -- between the makechrootpkg args and the makepkg args"