Feel free to edit anything in config.json and database.json.
You can override anything in the config.json or database.json using environment variables, which are interpreted as JSON.
For example, if you want to turn off GIF URL shortening without using the config file, simply set JURVUR_SHORTEN_GIF_URL to false.
Similarily, if you want to change the username, set JURVUR_USERNAME to Thomas, or whatever you want it to be. Note how you have to INCLUDE the s, because it's JSON.
It's JSON, so you can also set the channels, by setting JURVUR_CHANNELS to ["#channel1", "channel2"].
If you want to set a thing in database.json, simply use the prefix JURVUR_DATABASE_ instead of JURVUR_.
The preferred way to give the bot database info is making an environment variable called DATABASE_URL with info in the following format:
<dbtype>://<username>:<password>@<host>:<port>/<database>
Where <dbtype> is either postgres, sqlite or mysql. Remember to add the appropriate driver to config.json, or just set it with the JURVUR_DATABASE_DRIVER. Again, remember to put what you need to set in quotes (so the actual content of the environment variable actually has quotes)
The appropriate drivers are:
org.postgresql.Driver
com.mysql.jdbc.Driver
org.sqlite.JDBC
Running Jurvur on Heroku is very simple. It already includes a Procfile that you need, and automatically grabs the database needed. You should already know the basics of using Heroku, I won't go into detail on how to set a project up.