Added link to the default excluded files in README (#74)

- make it easy to find which files are not included by default

README.md

@@ -76,7 +76,7 @@ The `with` portion of the workflow **must** be configured before the action will
 | ------------- | ------------- | ------------- | ------------- |
 | `api-url`  | The base URL of your Ghost Admin API, found by configuring a new Custom Integration in Ghost Admin»Integrations | `secrets` | **Yes** |
 | `api-key`  | The authentication key for your Ghost Admin API, found by configuring a new Custom Integration in Ghost Admin»Integrations | `secrets` | **Yes** |
-| `exclude` | A list of files & folders to exclude from the generated zip file in addition to the defaults, e.g. `"gulpfile.js *dist/*"` | `string` | No |
+| `exclude` | A list of files & folders to exclude from the generated zip file in addition to the [defaults](https://github.com/TryGhost/action-deploy-theme/tree/main/index.js#L28), e.g. `"gulpfile.js *dist/*"` | `string` | No |
 | `theme-name` | A custom theme name that overrides the default name in package.json. Useful if you use a fork of Casper, e.g. `"my-theme"` | `string` | No |
 | `file` | Path to a built zip file. If this is included, the `exclude` and `theme-name` options are ignored | `string` | No |
 | `working-directory` | A custom directory to zip when a theme is in a subdirectory, e.g. `packages/my-theme` | `string` | No |