READMEの更新

[Npepperlinux]

• Snapパッケージの存在を明記しました
• Obtainiumへのリンクを追加しました
• FirefishをIceshrimpへ置き換えました
• 英文を一部編集しました

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 27.69%. Comparing base (6955662) to head (932c80d).
Report is 1 commits behind head on develop.

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Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #662   +/-   ##
========================================
  Coverage    27.69%   27.69%           
========================================
  Files          312      312           
  Lines        16253    16253           
========================================
  Hits          4501     4501           
  Misses       11752    11752           

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