Make the tutorial more beginner-friendly

[zhlsk]

At the recent Django Girls event in Amsterdam, some students struggled to follow the tutorial, especially when editing view.py, url.py and post_list.html. This was mainly because the tutorial does not indicate what the source code should look like after editing them. To address this issue, I suggest making the following changes:

• Display what blog/views.py should look like
• Display what blog/urls.py file should look like.
• Give more clear instrcutions on how to update the template file.