added README

cpln-common/README.md

@@ -0,0 +1,35 @@
+# cpln-common
+
+A shared Helm library chart providing common templates for Control Plane marketplace charts. Not deployable on its own — intended to be used as a dependency.
+
+## Usage
+
+### 1. Add the dependency
+
+In your chart's `Chart.yaml`:
+
+```yaml
+dependencies:
+  - name: cpln-common
+    version: 1.0.0
+    repository: "oci://ghcr.io/controlplane-com/templates"
+```
+
+### 2. Use the templates
+
+Replace the labeling helpers in your chart's `_helpers.tpl` with includes from `cpln-common`:
+
+```yaml
+tags:
+  {{- include "cpln-common.tags" . | nindent 4 }}
+```
+
+You can remove the `CHART.chart`, `CHART.selectorLabels`, and `CHART.tags` definitions from your `_helpers.tpl` entirely.
+
+## Available templates
+
+| Template | Description |
+|---|---|
+| `cpln-common.tags` | Full label set for all marketplace resources |
+| `cpln-common.selectorLabels` | `app.cpln.io/name` and `app.cpln.io/instance` labels |
+| `cpln-common.chart` | Slugified `chart-name-version` string |