which says
“Windows users should download swigwin-1.3.39 which includes a prebuilt
executable”
This is the correct advice.
Download the zip file and unpack it. In it you’ll swig.exe. You can then
run swig like this “C:/path/to/swig.exe …” or add the unpacked
directory to your PATH environment variable if you want to be able to
just type “swig …”
Then all you have to do is figure out SWIG. The docs are pretty dense
but have a reasonable introduction to the basics and some ruby-specific
issues.
As it gets more complex, other good sections to read are ‘swig basics’,
‘typemaps’, and, if you’re dealing with C++ objects, possibly
cross-language polymorphism in the Python section.