Document zugbildungsplan.json source

(db-infoscreen, see COPYING) and MIT (jquery, jqueryui, and marquee libraries;

see the respective files) licenses.  Attribution is appreciated.

Background Data Updates

---

db-infoscreen can use <https://lib.finalrewind.org/dbdb/db_zugbildung_v0.json>

to show scheduled ICE/IC types (ICE 1/2/3/4/T, IC 1/2), wagon orders, and other

attributes. It expects the file to be provided in `share/zugbildungsplan.json`.

As this information is updated regularly, the file is not shipped as part of

this db-infoscreen distribution. It is recommended to retrieve it a few minutes

after midnight via a daily cronjob. See `examples/dbf_update_zugbildungsplan`

for a shell script.

DBF will periodically reload `share/zugbildungsplan.json`. You can use your

service supervisor (e.g. `systemctl reload db-infoscreen`) to force an

immediate reload. You may also ignore the file entirely; it is entirely

optional.

System requirements

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#!/bin/sh

set -eu

wget -qO share/zugbildungsplan.json.new https://lib.finalrewind.org/dbdb/db_zugbildung_v0.json

chmod 644 share/zugbildungsplan.json.new

mv share/zugbildungsplan.json.new share/zugbildungsplan.json