chore: Update Arch README link to official repos

[BreD1810]

Description

glab has been added the the official Arch repos. This PR updates the README to reflect this.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation
• Chore (Related to CI or Packaging to platforms)

[codecov]

Codecov Report

Merging #937 (6d06b6a) into trunk (8a98e38) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            trunk     #937   +/-   ##
=======================================
  Coverage   59.50%   59.50%           
=======================================
  Files          97       97           
  Lines        7611     7611           
=======================================
  Hits         4529     4529           
  Misses       2680     2680           
  Partials      402      402           

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[zemzale]

Nice to see this.