Add Repo Size to README.md

[AliAlimohammadi]

@siriak, this is ready to be merged.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.76%. Comparing base (43299ac) to head (33592c3).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #980      +/-   ##
==========================================
- Coverage   95.77%   95.76%   -0.01%     
==========================================
  Files         351      351              
  Lines       22934    22934              
==========================================
- Hits        21964    21962       -2     
- Misses        970      972       +2     

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[siriak]

I don't think we need to add this badge, it doesn't add useful info to the user. The size is not a concern and it's almost always not a concern.