Add examples in README.md

[bkamins]

Fixes #78

[codecov]

Codecov Report

Merging #79 (639b54f) into main (53f57d4) will increase coverage by 1.51%.
The diff coverage is n/a.

❗ Current head 639b54f differs from pull request most recent head 0af16b2. Consider uploading reports for the commit 0af16b2 to get more accurate results

@@            Coverage Diff             @@
##             main      #79      +/-   ##
==========================================
+ Coverage   87.00%   88.51%   +1.51%     
==========================================
  Files           1        1              
  Lines         331      331              
==========================================
+ Hits          288      293       +5     
+ Misses         43       38       -5     

Impacted Files	Coverage Δ
src/PooledArrays.jl	88.51% <0.00%> (+1.51%)	⬆️

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