Add readme

Author: suda

README.md

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+### docker-postgres-pg-cron
+
+This repository builds Docker images that package PostgreSQL with the pg_cron extension across multiple base OS variants, and publishes multi-arch images for both amd64 and arm64.
+
+#### What you get
+- **PostgreSQL + pg_cron**: pg_cron is built/installed and ready to enable per database.
+- **Base OS variants**: Alpine (including specific minor versions) and Debian Trixie.
+- **Multi-arch**: Images are pushed as a manifest list covering amd64 and arm64; Docker automatically pulls the right image for your platform.
+
+#### Variants (by Dockerfile in this repo)
+- `Dockerfile.alpine`
+- `Dockerfile.alpine3.21`
+- `Dockerfile.alpine3.22`
+- `Dockerfile.trixie` (Debian Trixie)
+
+Tag names in your registry may follow a pattern like:
+- `postgres-<MAJOR>-alpine`
+- `postgres-<MAJOR>-alpine3.21`
+- `postgres-<MAJOR>-alpine3.22`
+- `postgres-<MAJOR>-trixie`
+
+Replace `<MAJOR>` with the PostgreSQL major version you want (e.g., `16`, `15`). See the GHCR package page for the authoritative list of available tags.
+
+### Quick pull instructions
+
+Images are published to GHCR under `ghcr.io/suda/docker-postgres-pg-cron`.
+
+```bash
+# Alpine latest for a major version (example: Postgres 16 on Alpine)
+docker pull ghcr.io/suda/docker-postgres-pg-cron:16-alpine
+
+# Specific Alpine base version
+docker pull ghcr.io/suda/docker-postgres-pg-cron:16-alpine3.22
+
+# Debian Trixie variant
+docker pull ghcr.io/suda/docker-postgres-pg-cron:16-trixie
+
+# Older major versions (examples)
+docker pull ghcr.io/suda/docker-postgres-pg-cron:15-alpine
+docker pull ghcr.io/suda/docker-postgres-pg-cron:15-trixie
+```
+
+Because these are multi-arch images, you do not need to specify architecture; Docker will pull the correct `amd64` or `arm64` image automatically based on your platform.
+
+### Enabling pg_cron in your database
+
+Once the container is running and you are connected to a database, enable the extension:
+
+```sql
+CREATE EXTENSION IF NOT EXISTS pg_cron;
+```
+
+You can then schedule jobs, for example:
+
+```sql
+SELECT cron.schedule('nightly-vacuum', '0 3 * * *', $$VACUUM$$);
+```
+
+### Example docker run
+
+```bash
+docker run -d \
+  --name pg-cron \
+  -e POSTGRES_PASSWORD=postgres \
+  -p 5432:5432 \
+  ghcr.io/suda/docker-postgres-pg-cron:16-alpine
+```
+
+Then connect with your preferred client and enable `pg_cron` as shown above.
+
+### Building locally (optional)
+
+If you want to build locally for testing, you can target a specific Dockerfile:
+
+```bash
+# Alpine 3.22 example
+docker build -f Dockerfile.alpine3.22 -t local/docker-postgres-pg-cron:postgres-16-alpine3.22 .
+
+# Debian Trixie example
+docker build -f Dockerfile.trixie -t local/docker-postgres-pg-cron:postgres-16-trixie .
+```
+
+Push and tag according to your registry conventions.
+
+
+### Troubleshooting
+
+If you see an error like:
+
+```
+Jobs must be scheduled from the database configured in cron.database_name
+```
+
+set the database `pg_cron` should run against by providing PostgreSQL server args via environment variable when starting the container:
+
+```bash
+docker run -d \
+  --name pg-cron \
+  -e POSTGRES_PASSWORD=postgres \
+  -e POSTGRES_ARGS="-c cron.database_name=YOUR_DB" \
+  -p 5432:5432 \
+  ghcr.io/suda/docker-postgres-pg-cron:16-alpine
+```
+
+Replace `YOUR_DB` with the target database name. Schedule jobs from that database after enabling `pg_cron`.
+
+