Fix typo & add citation file

[GavEdwards]

Summary

Fix typo where 'grouping' was misspelt 'groupping' and test an initial citation file

• [x] Code passes all tests
• [x] Unit tests provided for these changes
• [x] Documentation and docstrings added for these changes

Changes

• Fix typo where 'grouping' was misspelt 'groupping'
• test adding an initial citation file

[codecov-commenter]

Codecov Report

Merging #19 (2af71bc) into main (03c094e) will not change coverage. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main      #19   +/-   ##
=======================================
  Coverage   99.86%   99.86%           
=======================================
  Files          14       14           
  Lines         742      742           
=======================================
  Hits          741      741           
  Misses          1        1           

Impacted Files	Coverage Δ
tests/integration/test_aggregation.py	100.00% <ø> (ø)
rexmex/scorecard.py	100.00% <100.00%> (ø)

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[benedekrozemberczki]

Thank you!