Improve docs of boolean operations

[RubenRubens]

Display __or__ example as a block of code.

[codecov]

Codecov Report

Merging #737 (db998e4) into master (0f249df) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #737   +/-   ##
=======================================
  Coverage   94.64%   94.64%           
=======================================
  Files          32       32           
  Lines        7249     7249           
  Branches      789      789           
=======================================
  Hits         6861     6861           
  Misses        255      255           
  Partials      133      133           

Impacted Files	Coverage Δ
cadquery/cq.py	91.32% <ø> (ø)

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[jmwright]

Thanks again @RubenRubens !