Add warning for write level rights with regards to repo secrets (github#15553)

Author: mounilKshah

content/actions/security-guides/security-hardening-for-github-actions.md

@@ -48,6 +48,12 @@ To help prevent accidental disclosure, {% data variables.product.product_name %}
 - **Consider requiring review for access to secrets**
     - You can use required reviewers to protect environment secrets. A workflow job cannot access environment secrets until approval is granted by a reviewer. For more information about storing secrets in environments or requiring reviews for environments, see "[Encrypted secrets](/actions/reference/encrypted-secrets)" and "[Using environments for deployment](/actions/deployment/using-environments-for-deployment)."
 
+{% warning %}
+
+**Warning**: Any user with write access to your repository has read access to all secrets configured in your repository. Therefore, you should ensure that the credentials being used within workflows have the least privileges required.
+
+{% endwarning %}
+
 ## Using `CODEOWNERS` to monitor changes
 
 You can use the `CODEOWNERS` feature to control how changes are made to your workflow files. For example, if all your workflow files are stored in `.github/workflows`, you can add this directory to the code owners list, so that any proposed changes to these files will first require approval from a designated reviewer.