docs: explain PGDATA new values

[thomasboussekey]

and fix markdown warnings in README

[phillipross]

These code blocks seem to be rendering incorrectly. Maybe because they are indented?

[phillipross]

Typo fix opportunity: I believe "Recomendations" should be spelled "Recommendations"

[phillipross]

Thanks for fixing this and cleaning up. I've added two comments as requests for changes.

[ImreSamu]

Thank you very much for the PR!

I have two small pieces of feedback:

1.) For Postgres >=18 it is probably better to recommend using /var/lib/postgresql instead of /var/lib/postgresql/18/docker.
see: docker-library/postgres#1364 (comment)

I tested with:

• docker run -d -v $(pwd)/gisdata:/var/lib/postgresql -e POSTGRES_PASSWORD=test postgis/postgis:18-3.6

and inside the container the data is automatically placed in the new path:
fixing permissions on existing directory /var/lib/postgresql/18/docker ... ok
pg_ctl -D /var/lib/postgresql/18/docker -l logfile start

On the host I can also see the files created under ./gisdata/18/docker/:

# ls ./gisdata/18/docker/
base          pg_dynshmem    pg_logical    pg_replslot   pg_stat      pg_tblspc    pg_wal                postgresql.conf
global        pg_hba.conf    pg_multixact  pg_serial     pg_stat_tmp  pg_twophase  pg_xact               postmaster.opts
pg_commit_ts  pg_ident.conf  pg_notify     pg_snapshots  pg_subtrans  PG_VERSION   postgresql.auto.conf  postmaster.pid

So it looks like we should really follow the upstream suggestion, since that path is version-independent.
But please also double-check this on your side.

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I usually refresh the README.md table with the one generated by ./update.sh.
That means the current table formatting will be overwritten during the next update.
I just wanted to mention this in advance, so please don’t take it personally if the formatting gets replaced later.

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From the above, my first remark is probably the more important one.