missing man path

[Karl Berry]

    /opt/texlive/2020/bin/man     # option 2

Ok, when last night's update makes it around there should be a symlink
bin/man.

Always before everything under bin/ has been a platform name. I changed
the places I found in our code that were assuming that, but there may be
more, or in other people's code or procedures. If more problems are
reported, may have to rethink. --thanks, karl.