docs(readme): polish badges

[LitoMore]

Description

• Remove the duplicated old school Discord badge
• Update the Twitter/X badge and fix its logo (related to Add X icon simple-icons/simple-icons#9200)

[welcome]

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[orhun]

Why Discord badge was removed? 😢 I liked that one

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 42.00%. Comparing base (e13b158) to head (ecc864e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1159   +/-   ##
=======================================
  Coverage   42.00%   42.00%           
=======================================
  Files          21       21           
  Lines        1981     1981           
=======================================
  Hits          832      832           
  Misses       1149     1149           

Flag	Coverage Δ
unit-tests	42.00% <ø> (ø)

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[LitoMore]

Why Discord badge was removed? 😢 I liked that one

Ah, there is already a shields.io Discord badge below it. And the large one looks blur on Retina screens.

However, let me add it back if you'd like to keep it.

[orhun]

Thanks!

[welcome]

Congrats on merging your first pull request! ⛰️