update readme to reflect work on window functions

[jimexist]

Which issue does this PR close?

Closes #.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #471 (e6b8da5) into master (c794f2d) will not change coverage.
The diff coverage is n/a.

❗ Current head e6b8da5 differs from pull request most recent head a09262d. Consider uploading reports for the commit a09262d to get more accurate results

@@           Coverage Diff           @@
##           master     #471   +/-   ##
=======================================
  Coverage   75.41%   75.41%           
=======================================
  Files         153      153           
  Lines       25683    25683           
=======================================
  Hits        19370    19370           
  Misses       6313     6313           

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