Populate a fresh install of Vanilla with fake data for users, categories, discussions and comments.
Edit manifest.json to change the values for total users, categories, discussions and comments. You can also specify a different manifest file with the --manifest option.
Running the following command will get the ball rolling:
php colonize.php --database="vanilla" --host="localhost" --user="root"
Once complete, visit /dba/counts on your Vanilla install and update all items listed.