Update Readme(How to Library Download)

[LeoAndo]

The download process described in the readme has been updated to the latest.

https://github.com/PokeAPI/pokekotlin/releases/tag/2.3.1

[codecov]

Codecov Report

Merging #90 (2b11941) into main (9a06966) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##               main      #90   +/-   ##
=========================================
  Coverage     65.64%   65.64%           
  Complexity      106      106           
=========================================
  Files            19       19           
  Lines           885      885           
  Branches          3        3           
=========================================
  Hits            581      581           
  Misses          303      303           
  Partials          1        1           

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