[docs] Bad link to Ousterhout paper

[R. Drew Davis]

On http://docs.python.org/howto/advocacy.html in the references section,
there's a link for Ousterhout's scripting paper.   As given,

http://home.pacbell.net/ouster/scripting.html

the link doesn't work.   I guess the page moved.   The paper can now be
found at:

http://www.tcl.tk/doc/scripting.html

Please fix the link.

Thanks.

Drew