Dead link to osm2pgsql LUA transforms on main page of repository

[mboeringa]

Expected behavior

The Database schema change (v4.x) section of the main page contains a link to the "osm2pgsql lua transforms". This link should point to a valid page.

Actual behavior

Link is dead / invalid.

Links and screenshots illustrating the problem

Link to section with problem:
https://github.com/gravitystorm/openstreetmap-carto#database-schema-change-v4x

I guess with all the recent changes to osm2pgsql and its documentation, this link should now point to some subpage of:
https://osm2pgsql.org/

[mboeringa]

I now noticed the same dead link is also included in the 'openstreetmap-carto.lua' script part of the repository as a the first comment line, and would need updating as well.