Added instructions for Helm Action

Author: garethr

README.md

@@ -27,3 +27,38 @@ passed to the action using `with`, as demonstrated with `files` in the above exa
 | policy | policy | Where to find the policy folder or files |
 | namespace | main | The Rego namespace to use for testing |
 | output | stdout | How to format the output from Conftest (stdout, json or tap) |
+
+
+## Helm
+
+Conftest also has a [Helm plugin](https://github.com/instrumenta/helm-conftest) which makes testing Helm charts easier, and
+that plugin is also available as an Action.
+
+You can use the action as follows:
+
+```yaml
+on: push
+name: Validate
+jobs:
+  conftest:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: test
+      uses: instrumenta/conftest-action/helm@master
+      with:
+        chart: mysql
+```
+
+The Conftest Helm Action has a small number of properties which map to the parameters for Conftest itself. These are
+passed to the action using `with`, as demonstrated with `chart` in the above example.
+
+| Property | Default | Description |
+| --- | --- | --- |
+| chart | - | *Required* which chart directory to test |
+| policy | policy | Where to find the policy folder or files |
+| namespace | main | The Rego namespace to use for testing |
+| output | stdout | How to format the output from Conftest (stdout, json or tap) |
+
+
+