Add extra links to relevant sections in documentation.
Add example of using the new override location for rspamd.
Add clarification in rspamd section for rspamd override change and new autoconfig.* endpoint
Anything that can be configured in the web administration interface,
can also be configured via the Mailu RESTful API.
See the section Advanced configuration in the configuration reference
for the relevant settings in mailu.env for enabling the API.
(API, WEB_API, API_TOKEN).
