Merge pull request #91 from kddejong/docs/readme/parameter-override

Add parameter override docs in the README

Author: kddejong

README.md

@@ -18,7 +18,27 @@ Deploys AWS CloudFormation Stacks.
 
 The action can be passed a CloudFormation Stack `name` and a `template` file. The `template` file can be a local file existing in the working directory, or a URL to template that exists in an [Amazon S3](https://aws.amazon.com/s3/) bucket. It will create the Stack if it does not exist, or create a [Change Set](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/using-cfn-updating-stacks-changesets.html) to update the Stack. An update fails by default when the Change Set is empty. Setting `no-fail-on-empty-changeset: "1"` will override this behavior and not throw an error.
 
-See [action.yml](action.yml) for the full documentation for this action's inputs and outputs.
+### Inputs
+
+A few inputs are highlighted below. See [action.yml](action.yml) for the full documentation for this action's inputs and outputs.
+
+#### parameter-overrides (OPTIONAL)
+
+To override parameter values in the template you can provide a string or a file that is either local or an URL.
+
+Override multiple parameters separated by commas: `"MyParam1=myValue1,MyParam2=myValue2"`
+
+Override a comma delimited list: `"MyParam1=myValue1,MyParam1=myValue2"` or `MyParam1="myValue1,myValue2"`
+
+Override parameters using a local JSON file: `"file:///${{ github.workspace }}/parameters.json"` with a file named `parameters.json` at the root of the repository:
+```json
+[
+  {
+    "ParameterKey": "MyParam1",
+    "ParameterValue": "myValue1"
+  }
+]
+```
 
 > You can learn more about [AWS CloudFormation](https://aws.amazon.com/cloudformation/)