docs: clarify coveralls repo permissions (#182)

README.md

@@ -140,7 +140,7 @@ Ensure that:
 on: ["push", "pull_request"]
 ```
 
-2. You have invited the [@coveralls](https://github.com/coveralls) user to your repository as a collaborator
+2. You have invited the [@coveralls](https://github.com/coveralls) user to your repository with `Role: Write`
 3. You have enabled the "LEAVE COMMENTS?" setting in the "Pull Request Alerts" area in your Repo Settings page inside the Coveralls app.
 
 ### Coveralls responds with "cannot find matching repository"