Descriptive error message for anonymous gin get

[JuliaSprenger]

The gin-cli only permits to get public repositories when being logged in. The error message when trying to get a repository anonymously is

Downloading repository Repository download failed. Internal git command returned: Cloning into <REPO>...
[email protected]: Permission denied (publickey,keyboard-interactive).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
 
[error] 1 operation failed

I think it would be helpful to not only state this as a permission denied error, but also provide the hint that logging in using gin login might resolve the issue. This issue is related to #52