a minor update to makefile.mgw: Help Workshop

[Mojca M. <moj...@gm...>]

Hello,

during my failures to try to compile the gnuplot binary properly on
windows, I found out that the web reference to Help Workshop mentioned
in the makefile isn't working any more (I guess that the domain has
changed). It would be probably more helpful to mention that one should
try to download hcwsetup.exe from Microsoft web pages. (google for
"hcwsetup.exe site:microsoft.com")

Here's one page from where it can be downloaded, although I'm not 100%
sure that the link to it is stable:
http://download.microsoft.com/download/win95/MSPRESS/1.0/W9X/EN-US/hcwsetup.EXE

And some useful description:
http://www.microsoft.com/technet/prodtechnol/office/office2000/proddocs/opg/part2/ch13.mspx

Mojca