Fix triple asterisk in documentation

[PaulBrandUWV]

The documentation includes code examples, but since the * is reserved to make text look bold in robot documentation language, the headers in the examples only show a single asterisk * instead of the required triple asterisk ***

Before:

After:

Fixes: #385

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.87%. Comparing base (fac8933) to head (16ce8f1).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #395      +/-   ##
==========================================
+ Coverage   83.98%   87.87%   +3.89%     
==========================================
  Files           9        9              
  Lines         437      437              
  Branches      102      102              
==========================================
+ Hits          367      384      +17     
+ Misses         65       51      -14     
+ Partials        5        2       -3     

Flag	Coverage Δ
acceptance	83.98% <ø> (ø)
unit	61.09% <ø> (?)

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