Add permissions required to README.md (#64)

README.md

@@ -18,6 +18,28 @@ In order to use this action, you will need to generate a JSON file using the fol
 ]
 ```
 
+## Permissions
+
+It is possible you have a `GITHUB_TOKEN` with restricted access by default, in which case you might get the following error:
+
+```
+Error: GitHubApiUnauthorizedError: Unable to create a check, please make sure that the provided 'repo-token' has write permissions to 'your/repo' - cause: HttpError: Resource not accessible by integration
+```
+
+You need to provide the `checks` write permission:
+
+```yaml
+permissions:
+  checks: write
+```
+
+You can use `permissions` either as a top-level key, to apply to all jobs in the workflow, or within specific jobs.
+When you add the permissions key within a specific job, all actions and run commands within that job that use the `GITHUB_TOKEN` gain the access rights you specify.
+
+**IMPORTANT**: Setting a `permissions` field will disable all omitted permissions, like the `contents: read`, which is needed to clone and read your repository.
+
+You can learn more about `GITHUB_TOKEN` permissions at: https://docs.github.com/en/actions/security-guides/automatic-token-authentication#permissions-for-the-github_token
+
 ## Inputs
 
 ### `repo-token`