Dosctring examples

[jGaboardi]

This PR addresses #6.

[codecov]

Codecov Report

Merging #16 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master     #16   +/-   ##
======================================
  Coverage    85.2%   85.2%           
======================================
  Files           4       4           
  Lines         244     244           
  Branches       55      55           
======================================
  Hits          208     208           
  Misses         17      17           
  Partials       19      19           

Impacted Files	Coverage Δ
nhgisxwalk/geocrosswalk.py	97.7% <ø> (ø)

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