Re-write the settings docs

[Mark Walker]

The table that's in use on the settings docs doesn't read very nicely/easily given the length of settings names and the amount of information that corresponds with each one.

https://django-sql-explorer.readthedocs.io/en/latest/settings.html

This could look, and read, much better if it was displayed differently, perhaps in sections for each setting.

[Pankaj Patil]

I would love to take this up @marksweb.