Add CITATION.cff

[eggplants]

Closes: #165

[codecov]

Codecov Report

Merging #166 (d36f741) into master (d6ef550) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #166   +/-   ##
=======================================
  Coverage   95.46%   95.46%           
=======================================
  Files          10       10           
  Lines         661      661           
=======================================
  Hits          631      631           
  Misses         30       30           

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