docs: mark bok-choy as deprecated

[kdmccormick]

Pending acceptance of openedx/public-engineering#13

[codecov]

Codecov Report

Merging #364 (07dc291) into master (c70246c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #364   +/-   ##
=======================================
  Coverage   86.13%   86.13%           
=======================================
  Files          11       11           
  Lines         952      952           
  Branches      176      176           
=======================================
  Hits          820      820           
  Misses         88       88           
  Partials       44       44           

Flag	Coverage Δ
unittests	86.13% <ø> (ø)

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[feanil]

Just need to fix the commit message.