Add sponsors section to README

[rmcdaniel]

Added a sponsors section to acknowledge community support.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (1216fdf) to head (4fb1269).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##              master      #306   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity       350       350           
===========================================
  Files             49        49           
  Lines           1443      1443           
===========================================
  Hits            1443      1443           

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