[docs] add section on unbounded rays

[odow]

x-ref https://discourse.julialang.org/t/getting-unbounded-ray-in-jump/126097

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.58%. Comparing base (2d26cdb) to head (ca7fb47).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3945   +/-   ##
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  Coverage   99.58%   99.58%           
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  Files          43       43           
  Lines        6066     6066           
=======================================
  Hits         6041     6041           
  Misses         25       25           

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