Add information how to install via homebrew

[marciniwanicki]

Issue number of the reported bug or feature request: #3

Updated the documentation with short instruction how to install xcdiff via Homebrew.

[codecov]

Codecov Report

Base: 96.71% // Head: 96.71% // No change to project coverage 👍

Coverage data is based on head (3a75d69) compared to base (289872e).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #126   +/-   ##
=======================================
  Coverage   96.71%   96.71%           
=======================================
  Files          50       50           
  Lines        2773     2773           
=======================================
  Hits         2682     2682           
  Misses         91       91           

Impacted Files	Coverage Δ
Sources/XCDiffCommand/CommandRunner.swift	97.36% <100.00%> (ø)
...es/XCDiffCore/Comparator/CopyFilesComparator.swift	99.28% <100.00%> (ø)
...XCDiffCore/Comparator/DependenciesComparator.swift	97.80% <100.00%> (ø)
...ffCore/Comparator/ResolvedSettingsComparator.swift	98.75% <100.00%> (ø)
...es/XCDiffCore/Comparator/RunScriptComparator.swift	100.00% <100.00%> (ø)
...e/Library/Descriptors/SwiftPackageDescriptor.swift	89.65% <100.00%> (ø)
...es/XCDiffCore/Library/SettingValueComparator.swift	100.00% <100.00%> (ø)
Sources/XCDiffCore/Library/SettingsHelper.swift	94.33% <100.00%> (ø)
...iffCore/ResultRenderer/Renderer/HTMLRenderer.swift	100.00% <100.00%> (ø)

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[kwridan]

🎉

[kwridan]

The release documentation could do with an update too to outline how to update Homebrew as well.