Black borders with table using \markuplist and please center

[Adam Good]

Hi Everyone,
I can make this pretty little table, see below but could someone please
help me add borders / gridlines around the cells? And, I'd like to be able
to center the table to the middle of the page.

Thank you in advance!
Adam

%%%
\markuplist {
  \override #'(padding . 4)
  \table #'(0 0 0)
    {
      %\underline { right-aligned center-aligned left-aligned }
      "1" "2" "3"
      "4" "" "6"
      "7" "8" ""
      "10" "" "12"
    }
}