add forked repo secrets notice to readme

README.md

@@ -23,7 +23,7 @@ steps:
     yml: ./codecov.yml #optional
     fail_ci_if_error: true #optional (default = false)
 ```
->**Note**: This assumes that you've set your Codecov token inside *Settings > Secrets* as `CODECOV_TOKEN`. If not, you can [get an upload token](https://docs.codecov.io/docs/frequently-asked-questions#section-where-is-the-repository-upload-token-found-) for your specific repo on [codecov.io](https://www.codecov.io). 
+>**Note**: This assumes that you've set your Codecov token inside *Settings > Secrets* as `CODECOV_TOKEN`. If not, you can [get an upload token](https://docs.codecov.io/docs/frequently-asked-questions#section-where-is-the-repository-upload-token-found-) for your specific repo on [codecov.io](https://www.codecov.io). Keep in mind that secrets are *not* available to forks of repositories. 
 
 ## Arguments