SBE process: explain steps also with example

We describe the steps already, but there is no running example. That would help.

We should also describe when to add the hardware mapping, when to add the timed versions of timers, etc.

We could refer to it in the documentation of the controller checker, as it won't produce good results if the hardware mapping is absent (see #977 (closed)/!1051 (merged)).

Addresses #892