Remove README.md as packaged data in the wheel

[TheLonelyGhost]

README.md is not needed here except for reading to provide the long_description attribute in setup.py, which is then used only when uploading to pypi. It seems we can safely remove it from the manifest while retaining it in git.

Normally the data published here is for non-python files necessary for the program to function (e.g., i18n translations).

[codecov[bot]]

Codecov Report

Merging #16 into master will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##            master       #16   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           48        48           
  Lines         2621      2621           
=========================================
  Hits          2621      2621           

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