Minor cleanups, updates and clarifications. Also removes (incomplete
and well-known) build steps from README, as they are better described
in INSTALL.

* Made structure with headlines,
* reordered,
* kicked out 'What is missing' part,
* Updated content by home page site and user docs

They have different behavior w.r.t. filtered routes that are kept.

(and minor changes in documentation)

Also testing whether syncmail works.

Unless you object, I'll announce it today (9.5.) at noon.