doc/primer.rst: introspective example additional note

[marcus7070]

Will close #838.

[codecov]

Codecov Report

Merging #839 (f817939) into master (7afbb37) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #839   +/-   ##
=======================================
  Coverage   95.15%   95.15%           
=======================================
  Files          32       32           
  Lines        7495     7495           
  Branches      799      799           
=======================================
  Hits         7132     7132           
  Misses        224      224           
  Partials      139      139           

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[jmwright]

Looks good, thanks.

[jmwright]

Going ahead and merging this docs change.

[jmwright]

Thanks @marcus7070