Add more to README (#9)

* Add more to README

* Add link to workflows

* Update link

README.md

@@ -1,10 +1,11 @@
 # ESPHome Build action
 
-## inputs
+![GitHub release (latest SemVer)](https://img.shields.io/github/v/release/esphome/build-action)
 
-### `yaml_file`
 
-**Required**. The YAML filename to be compiled.
+This action takes a yaml file for an ESPHome device and will compile and output
+the build firmware file and a partial `manifest.json` file that can be used to flash 
+a device via [ESP Web Tools](https://esphome.github.io/esp-web-tools).
 
 ## Example usage
 
@@ -15,3 +16,22 @@ with:
   yaml_file: my_configuration.yaml
 
 ```
+
+This action is used by the [ESPHome publish workflow](https://github.com/esphome/workflows/blob/main/.github/workflows/publish.yml) that is used to compile firmware and publish simple GitHub pages sites for projects.
+
+## Inputs
+
+Name | Default | Description  
+-----|---------|------------
+`yaml_file` | _None_   | The YAML file to be compiled.
+`version`   | `latest` | The ESPHome version to build using.
+
+## Outputs
+
+Name   | Description  
+-------|------------
+`name` | The name of the device in yaml with the platform (eg. ESP32 or ESP8266) appended.
+
+## Output files
+
+This action will output a folder named with the output `name` and will contain two files, `{name}.bin` and `manifest.json`.