bug#70599: join vs. numeric order

[Dan Jacobson]

(info "(coreutils) Sorting files for join") needs to talk about numeric
order.

$ seq 111|join --check-order - /dev/null
join: -:10: is not sorted: 10

So the info manual needs to mention 'Even though your files might be in
perfect "sort --numeric-sort" order, you need to make them into plain
"sort" order first. Sorry. At least you'll get the same number of joins.'

Or, add a new join -n option. The join man page could now say:
'-n: use numeric comparisons. Note sort order also needs to be "sort -n" order.'

And / or mention how the user might tinker with LC_NUMERIC and / or
LC_COLLATE to somehow achieve numeric sorting...