Improve how posts look in the admin

The way posts are rendered in the Django Admin does not provide any helpful information about the post or its author. Change how the Admin displays the post information. We can display the post author's username when the post was created and a few characters of the post body. This is a straightforward change that can be made by adding a __str__() method to the Post Model.

This is what we currently have:

We want to have something like this: