Add comment about perl in README.md

[GBuella]

See: #5

Document in Readme.md what each dependancy is used for.
"perl -- for checking code style errors (or something similar)"

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Codecov Report

Merging #22 into master will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff          @@
##           master   #22   +/-   ##
====================================
  Coverage      75%   75%           
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  Files          10    10           
  Lines         172   172           
  Branches       21    21           
====================================
  Hits          129   129           
  Misses         29    29           
  Partials       14    14

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