docs: enhance external repository section

#245 #318

README.md

@@ -349,7 +349,7 @@ For example:
 You can use `deploy_key` or `personal_token`.
 When you use `deploy_key`, set your private key to the repository which includes this action and set your public key to your external repository.
 
-Be careful, `GITHUB_TOKEN` has no permission to access to external repositories.
+**Be careful, `GITHUB_TOKEN` has no permission to access to external repositories. Please create a personal access token and set it to `personal_token` like `personal_token: ${{ secrets.PERSONAL_TOKEN }}`.**
 
 ### ⭐️ Force orphan