Update rule doc for SwallowedException config

[schalkms]

This update explains the reason behind the config defaults.

Related to #3524

[codecov]

Codecov Report

Merging #3547 (200e843) into master (bdceacb) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #3547   +/-   ##
=========================================
  Coverage     77.53%   77.53%           
  Complexity     2829     2829           
=========================================
  Files           464      464           
  Lines          8769     8769           
  Branches       1713     1713           
=========================================
  Hits           6799     6799           
  Misses         1046     1046           
  Partials        924      924           

Impacted Files	Coverage Δ	Complexity Δ
...osch/detekt/rules/exceptions/SwallowedException.kt	77.35% <ø> (ø)	19.00 <0.00> (ø)

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