pg_upgrade "configdir" vs "datadir"

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/11/pgupgrade.html
Description:

pg_upgrade seems to assume that the datadir and the configdir are the same
but on Debian/Ubuntu they are not the same by default (installing from the
postgres repository).

The current documentation:

-d configdir
--old-datadir=configdir

the old database cluster configuration directory; environment variable
PGDATAOLD

-D configdir
--new-datadir=configdir

the new database cluster configuration directory; environment variable
PGDATANEW

In order for this to work on Debian/Ubuntu you need to also pass some
options with the actual configuration directory. For example:

-o 'config_file=/etc/postgresql/9.6/main/postgresql.conf'
-O 'config_file=/etc/postgresql/10/main/postgresql.conf'

I think the documentation could use some clarification on this point.