docs: CONTRIBUTING.md の改定

[m1sk9]

Details of implementation (実施内容)

1056 マージ以降, OreOreBot2 の開発環境は大きく変わったのでそれに合わせるために CONTRIBUTING.md を改定しました.

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Codecov Report

Merging #1072 (796cef7) into main (b41c397) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1072   +/-   ##
=======================================
  Coverage   73.89%   73.89%           
=======================================
  Files          75       75           
  Lines        5195     5195           
  Branches      459      459           
=======================================
  Hits         3839     3839           
  Misses        898      898           
  Partials      458      458           

Flag	Coverage Δ
unittests	73.89% <ø> (ø)

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