[latexrefman] document home page link

[Karl Berry]

No energy to write everything down right now, but I think the best
approach for the link to our home page is to use the
supposedly-supported "About" button (would be next to
"[Contents][Index]"). I couldn't figure out why the config variables I
tried didn't do the job from the doc and Texinfo's HTML.pm. Will have to
try some more tomorrow or ask help-texinfo ... I played around with the
css a bit independently of that per my weird ideas. --best, karl.