docs: add helm chart readme

helm/ember/README.md

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+# ember helm chart
+
+deploy [ember](https://github.com/kacy/ember) on kubernetes.
+
+## install
+
+```bash
+helm install my-ember ./helm/ember
+```
+
+with custom values:
+
+```bash
+helm install my-ember ./helm/ember \
+  --set ember.maxMemory=256mb \
+  --set ember.requirepass=secret \
+  --set resources.limits.memory=512Mi
+```
+
+## uninstall
+
+```bash
+helm uninstall my-ember
+```
+
+## configuration
+
+| parameter | description | default |
+|-----------|-------------|---------|
+| `replicaCount` | number of pod replicas | `1` |
+| `image.repository` | container image name | `ember` |
+| `image.tag` | image tag | `latest` |
+| `image.pullPolicy` | image pull policy | `IfNotPresent` |
+| `service.type` | kubernetes service type | `ClusterIP` |
+| `service.port` | service port | `6379` |
+| `ember.port` | ember listen port | `6379` |
+| `ember.metricsPort` | prometheus metrics port | `9100` |
+| `ember.maxMemory` | max memory limit (e.g. `256mb`) | `""` (unlimited) |
+| `ember.evictionPolicy` | eviction policy when memory is full | `noeviction` |
+| `ember.appendonly` | enable AOF persistence | `false` |
+| `ember.appendfsync` | AOF fsync policy (`always`, `everysec`, `no`) | `everysec` |
+| `ember.concurrent` | use concurrent mode instead of sharded | `false` |
+| `ember.requirepass` | require password for client connections | `""` (disabled) |
+| `resources` | CPU/memory resource requests and limits | `{}` |
+| `serviceAccount.create` | create a service account | `true` |
+| `serviceAccount.name` | override service account name | `""` |
+
+## examples
+
+### production with memory limits and auth
+
+```yaml
+# values-prod.yaml
+replicaCount: 1
+
+ember:
+  maxMemory: 1gb
+  evictionPolicy: allkeys-lru
+  appendonly: true
+  appendfsync: everysec
+  requirepass: "my-secret-password"
+
+resources:
+  limits:
+    cpu: "4"
+    memory: 2Gi
+  requests:
+    cpu: "1"
+    memory: 1Gi
+```
+
+```bash
+helm install ember-prod ./helm/ember -f values-prod.yaml
+```
+
+### development (no persistence, no auth)
+
+```bash
+helm install ember-dev ./helm/ember \
+  --set resources.limits.memory=256Mi
+```