Docker README: warn that postgres:latest moves to new major versions (#9529)

* Docker README: pin the PostgreSQL example to postgres:18

The docker run example starts the bare postgres image with its data at
/var/lib/postgresql. postgres:latest is expected to move to PostgreSQL 19
on its planned release date, November 19, 2026, and the 19 release
candidate image exits before starting on PostgreSQL 18 data in that
layout. postgres:18 is the same image as latest today and the version
Docker/freshrss/docker-compose-db.yml already uses.

* Docker README: keep postgres:latest and warn about major versions

Per review: instead of pinning the example to one PostgreSQL version,
keep the bare postgres image and add a note that latest moves to each
new major version, which refuses to start on the previous major's data,
and point to the Migrate database section.

* Docker README: apply review rewording of the postgres:latest note

Apply the suggested wording from review, with the docker-library/postgres#37
link pointing to that issue.

Co-authored-by: Alexandre Alapetite <alexandre@alapetite.fr>

CyberNative AI LLC
hello@cybernative.ai

CREDITS.md

@@ -79,6 +79,7 @@ People are sorted by name so please keep this order.
 * [Cron](https://github.com/featurecreep-cron): [contributions](https://github.com/FreshRSS/FreshRSS/pulls?q=is:pr+author:featurecreep-cron)
 * [Crupuk](https://github.com/Crupuk): [contributions](https://github.com/FreshRSS/FreshRSS/pulls?q=is:pr+author:Crupuk)
 * [Cyb10101](https://github.com/Cyb10101): [contributions](https://github.com/FreshRSS/FreshRSS/pulls?q=is:pr+author:Cyb10101)
+* [CyberNativeAI](https://github.com/CyberNativeAI): [contributions](https://github.com/FreshRSS/FreshRSS/pulls?q=is:pr+author:CyberNativeAI)
 * [Damien Leroy](https://github.com/ShiiFu): [contributions](https://github.com/FreshRSS/FreshRSS/pulls?q=is:pr+author:ShiiFu)
 * [Damstre](https://github.com/Damstre): [contributions](https://github.com/FreshRSS/FreshRSS/pulls?q=is:pr+author:Damstre)
 * [danc](https://github.com/danc): [contributions](https://github.com/FreshRSS/FreshRSS/pulls?q=is:pr+author:danc), [Web](http://tintouli.free.fr/)

Docker/README.md

@@ -213,6 +213,10 @@ docker run -d --restart unless-stopped --log-opt max-size=10m \
   --name freshrss-db postgres
 ```
 
+> ⚠️ `postgres` without a version tag is `postgres:latest`, which moves to each new major version of PostgreSQL.
+> New major versions of PostgreSQL refuse to start with the data of a different PostgreSQL version:
+> see update guidance on [docker-library/postgres#37](https://github.com/docker-library/postgres/issues/37) or with FreshRSS own [database migration](#migrate-database).
+
 In the FreshRSS setup, you will then specify the name of the container (`freshrss-db`) as the host for the database.
 
 See also the section [Docker Compose with PostgreSQL](#docker-compose-with-postgresql) below.