Reactor module readme update

[meiao]

Overview

Some clarification on the reactor-3.3.0 module. Why it is the way it is and when it should be loaded.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.62%. Comparing base (074363b) to head (a517054).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #2260   +/-   ##
=========================================
  Coverage     70.61%   70.62%           
+ Complexity    10020    10019    -1     
=========================================
  Files           844      844           
  Lines         40507    40507           
  Branches       6140     6140           
=========================================
+ Hits          28605    28608    +3     
+ Misses         9122     9120    -2     
+ Partials       2780     2779    -1     

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