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 :white_check_mark:

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

```diff @@ 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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