Update README to reflect bundled qd

[pllim]

• setup.py build is legacy command.
• qd has been bumped in Update built-in libqd to version 2.3.24 #258

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.28%. Comparing base (5de7fc7) to head (c2d4ed4).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #267   +/-   ##
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  Coverage   81.28%   81.28%           
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  Files           5        5           
  Lines        1010     1010           
=======================================
  Hits          821      821           
  Misses        189      189           

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[jhunkeler]

setup.py build is legacy command.

Shouldn't this be replaced with USE_SYSTEM_QD=1 pip install .? USE_SYSTEM_QD is an environment variable.

[pllim]

I thought life would be more exciting if they have to search how to install themselves, but ok.