Explain requirements for variables in settings.py

We have some variables needed in src/settings.py that are pretty straightforward to deal with (like SMTP_PORT) but others need some comment/explanation so folks know what they are supposed to so. Two examples that come to mind right now:

1. We should mention that the onionoo job interval specified is in minutes.
2. We should give some hint as to whether there are some needs for the JWT_SECRET. Could it just be "test1234" or some other text or does it need to be formatted particularly or...?

Apart from those two we might want to think whether other variables would benefit from a comment having in mind someone needing to set this app up who might not know all of the nitty-gritty details involved in it.