man -> html partially broken

[teuben]

The "make docs" (in man) is partially broken. The index files are empty. the individual html man pages are ok.
It uses rman (PolyglotMan). V3.2
It works on Ubuntu16, but not 18, not 20. The same version (2003!) of rman is however present on all these systems.

[teuben]

silly fix: path was wrong, needed ./ reference.