docs(clean): add docs for clean_country()

[ryanwdale]

Description

Added documentation for the clean_country and validate_country functions.

closes #398

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Snapshots:

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Checklist:

• My code follows the style guidelines of this project
• I have already squashed the commits and make the commit message conform to the project standard.
• I have already marked the commit with "BREAKING CHANGE" or "Fixes #" if needed.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[codecov]

Codecov Report

Merging #401 into develop will increase coverage by 0.04%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #401      +/-   ##
===========================================
+ Coverage    74.18%   74.22%   +0.04%     
===========================================
  Files           65       65              
  Lines         4804     4804              
===========================================
+ Hits          3564     3566       +2     
+ Misses        1240     1238       -2     

Impacted Files	Coverage Δ
dataprep/eda/distribution/render.py	68.35% <0.00%> (+0.25%)	⬆️

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[brandonlockhart]

Very well written, great job Ryan!