Update README.md

doc/ci/ssh_keys/README.md

@@ -30,7 +30,8 @@ This is the universal solution which works with any type of executor
 ## SSH keys when using the Docker executor
 
 You will first need to create an SSH key pair. For more information, follow the
-instructions to [generate an SSH key](../../ssh/README.md).
+instructions to [generate an SSH key](../../ssh/README.md). Do not add a comment
+to the ssh key, or the `before_script` will prompt for a passphrase.
 
 Then, create a new **Secret Variable** in your project settings on GitLab
 following **Settings > Variables**. As **Key** add the name `SSH_PRIVATE_KEY`