Document parameters in readme

[dstuebe]

Readme Only Changes!

• Add documentation to the Readme about how parameters are handled in AASM events per Does state name passing with parameter on event make sense?  #324

[codeclimate]

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[codecov-io]

Codecov Report

Merging #722 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #722   +/-   ##
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  Coverage   95.33%   95.33%           
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  Files          35       35           
  Lines        1242     1242           
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  Hits         1184     1184           
  Misses         58       58           

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[anilmaurya]

@dstuebe Thank you for contributing 👍