smtp_tls setting for ini file wrong in usage.md and docs

[edwhardo]

What an awesome project!
I noticed the commit for smtp_tls so I moved all of the previously categorized INVALID smtp_tls emails back to the Inbox in hope that they'd be processed.
They were definitely processed and moved in to a new folder, aptly named SMTP_TLS.

I realized nothing would display in grafana because the dashboard hasn't been upgraded, so I tried looking for indexes in elasticsearch and couldn't see any. Then, I had a look in cli.py and noticed that I was missing an entry from the ini file. The following needs to be in the section
[general]
save_smtp_tls = True

[edwhardo]

I closed the issue because I thought it was in the docs, but have now re-opened it because I noticed docs and usage say "save_smtp_sts"
but should be "save_smtp_tls"
The latter is in the code (e.g. cli.py)

[AnaelMobilia]

@edwhardo 0fa6beb should have resolve your last comment :)

Regards