document server update

[dthv]

This issue serves as reminder that I shall document basic instructions for manual updates.

Essentially, only server/planar.sqlite, server/server_config.cfg, server/static/assets need to be preserved/carried over to the new version.

[develroo]

Maybe add a path for certs as well. I currently have this set up in my docker instance, and I use letsencrypt to provide the certs.