Add example database, updated readme, added delete_post.php.

I added an example database with chirps, users, following, likes, reposts, and replies tables. Some of the column definitions may not be correct but everything works fine to post with this database. I updated the readme with instructions on how to use the database. A post request to delete_post.php with ?chirp=<id> will replace the chirp content with "This chirp is not available." There is also code that would fully remove the post. @smileyzone on chirp