docs: Add an "other R packages" section

[trevorld]

closes #45

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.09%. Comparing base (d783e1e) to head (18ae1d4).
⚠️ Report is 47 commits behind head on master.
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Additional details and impacted files

@@            Coverage Diff             @@
##           master      #56      +/-   ##
==========================================
- Coverage   99.54%   98.09%   -1.45%     
==========================================
  Files           1        2       +1     
  Lines         219      473     +254     
==========================================
+ Hits          218      464     +246     
- Misses          1        9       +8     

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