chore: add warning note about broken v3.1.0 version

README.md

@@ -6,6 +6,11 @@
 
 A GitHub action that publishes your code coverage to [Code Climate](http://codeclimate.com/).
 
+> **Warning**
+>
+> Please upgrade to v3.1.1 immediately. v3.1.0 was recently broken inadverdently, and the only fix is to upgrade your action to v3.1.1. Please see [#626](https://github.com/paambaati/codeclimate-action/issues/626) for more details.
+
+
 ## Usage
 
 This action requires that you set the [`CC_TEST_REPORTER_ID`](https://docs.codeclimate.com/docs/configuring-test-coverage) environment variable. You can find it under Repo Settings in your Code Climate project.