Add Ecu automaton documentation

[polybassa]

This PR just adds documentation

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 81.68%. Comparing base (86f034b) to head (4e684d0). Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4499      +/-   ##
==========================================
+ Coverage   81.64%   81.68%   +0.03%     
==========================================
  Files         337      355      +18     
  Lines       84604    84871     +267     
==========================================
+ Hits        69074    69325     +251     
- Misses      15530    15546      +16     

see 268 files with indirect coverage changes