Added README.md for postgresqlcluster chart.

Author: pantierra

charts/postgrescluster/README.md

@@ -0,0 +1,78 @@
+# PostgresCluster Helm Chart
+
+A Helm chart wrapper for deploying PostgreSQL clusters using [CrunchyData's PostgreSQL Operator (PGO)](https://access.crunchydata.com/documentation/postgres-operator/).
+
+## Purpose
+
+This chart creates `PostgresCluster` custom resources that are managed by PGO. It serves as a configuration layer between eoAPI and the PostgreSQL operator, providing:
+
+- **PostGIS support** for geospatial data
+- **PgBouncer** connection pooling
+- **Configurable backups** (S3, GCS, Azure, or volume-based)
+- **eoAPI-specific defaults** for schema permissions and database setup
+
+## Prerequisites
+
+Install the PostgreSQL Operator first:
+
+```bash
+helm install --set disable_check_for_upgrades=true pgo \
+  oci://registry.developers.crunchydata.com/crunchydata/pgo \
+  --version 5.7.4
+```
+
+## Usage
+
+This chart is typically used as a dependency of the main eoAPI chart:
+
+```yaml
+# In eoAPI's Chart.yaml
+dependencies:
+  - name: postgrescluster
+    version: 5.7.4
+    repository: "https://devseed.com/eoapi-k8s/"
+    condition: postgrescluster.enabled
+```
+
+### Standalone Installation
+
+```bash
+helm install my-postgres ./charts/postgrescluster \
+  --set postgresVersion=16 \
+  --set postGISVersion=3.4
+```
+
+## Key Configuration
+
+| Parameter | Description | Default |
+|-----------|-------------|---------|
+| `postgresVersion` | PostgreSQL version | `16` |
+| `postGISVersion` | PostGIS version | `3.4` |
+| `pgBouncerReplicas` | Number of PgBouncer instances | `1` |
+| `backupsEnabled` | Enable pgBackRest backups | `false` |
+| `instances` | PostgreSQL instance configuration | See values.yaml |
+
+### Instance Configuration
+
+```yaml
+instances:
+  - name: postgres
+    replicas: 2  # High availability with 2 replicas
+    dataVolumeClaimSpec:
+      accessModes: ["ReadWriteOnce"]
+      resources:
+        requests:
+          storage: 10Gi
+```
+
+### Backup Configuration
+
+```yaml
+backupsEnabled: true
+s3:
+  bucket: "my-backups"
+  endpoint: "s3.amazonaws.com"
+  region: "us-east-1"
+  key: "ACCESS_KEY_ID"
+  keySecret: "SECRET_ACCESS_KEY"
+```