doc: README for numaflow-python project

[vigith]

Kindly explain what this PR does.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.63%. Comparing base (40cbff8) to head (a25cb39).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #259   +/-   ##
=======================================
  Coverage   93.63%   93.63%           
=======================================
  Files          65       65           
  Lines        2907     2907           
  Branches      152      152           
=======================================
  Hits         2722     2722           
  Misses        135      135           
  Partials       50       50           

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