tie configuration documentation

[Jay Anderson]

It may be useful to explain a little better what the tie-configuration
list pairs mean. It wasn't obvious to me from the documentation.
Here's what I found from trial and error:

The first value is the offset from the center of the staff. The second
value indicates the direction of the tie: 1=>up, -1=>down, 0=>center.
A non-pair entry in the list will cause said tie to be formatted
automatically (already documented).

Here's how I used it,
   <<
     \context Voice="1"
     {
       \voiceOne
       \override TieColumn #'tie-configuration =
         #'((-2.5 . 1) (-8.5 . -1))
       <fis a,>4.~ <fis a,>4 <g ees>8
     }
     {
       \voiceTwo
       \once \override NoteColumn #'force-hshift = #1.7
       d8 cis d ees d g,
     }
   >> \oneVoice |

A minor improvement but it would have saved me a bit of time. I also
didn't find it right away as it's not near tie in the internals
reference. Perhaps a short example would be nice to have as part of
the manual. (similar to what I have above or a simpler one) Thanks
again!

-----Jay Anderson