visidata.org/man 404s now

❯ git grep visidata.org/man
CHANGELOG.md:        - replace .rst userguide with VisiData [man page](http://visidata.org/man)
README.md:* [Quick reference](https://visidata.org/man) (available within `vd` with `Ctrl+H`), which has a list of commands and options.
visidata/main.py:            print('  see https://visidata.org/man for full reference')