add research notice to readme

[yochannah]

... so contributors are aware this repo is participating in a study and metrics will be gathered over the next year :)

[codecov-commenter]

Codecov Report

Merging #431 (ad188b2) into master (f3e8bca) will not change coverage.
The diff coverage is n/a.

❗ Current head ad188b2 differs from pull request most recent head ebe4a8b. Consider uploading reports for the commit ebe4a8b to get more accurate results

@@           Coverage Diff           @@
##           master     #431   +/-   ##
=======================================
  Coverage   74.65%   74.65%           
=======================================
  Files          83       83           
  Lines       10063    10063           
=======================================
  Hits         7513     7513           
  Misses       2550     2550           

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