DOC: Add missing periods to the ArviZ community page

[star1327p]

Description

Add missing periods to the ArviZ community page.

Checklist

• Follows official PR format
• Includes a sample plot to visually illustrate the changes (only for plot-related functions)
• New features are properly documented (with an example if appropriate)?
• Includes new or updated tests to cover the new feature
• Code style correct (follows pylint and black guidelines)
• Changes are listed in changelog

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📚 Documentation preview 📚: https://arviz--2426.org.readthedocs.build/en/2426/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.75%. Comparing base (e5575b5) to head (feb8b35).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2426   +/-   ##
=======================================
  Coverage   86.75%   86.75%           
=======================================
  Files         124      124           
  Lines       12938    12938           
=======================================
  Hits        11224    11224           
  Misses       1714     1714           

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