Updated README.md to mention Arch packages

[randrej]

Added Arch Linux installation instructions to readme.

Since I didn't change any code, just added a link, I don't think this warrants an addition to the changelog or AUTHORS.

Description

Checklist

• [ ] I've added this contribution to the CHANGELOG file.
• [ ] I've added my name to the AUTHORS file (or it's already there).

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@08d6953). Click here to learn what that means. The diff coverage is n/a.

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  Hits              ?      886           
  Misses            ?      421           
  Partials          ?        0

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[amjith]

Thank you! :ice_cream: