[docs] add bounds to big-M examples

[odow]

x-ref #3703 (comment)

cc @remi-garcia

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.42%. Comparing base (177d213) to head (f54df52).

Additional details and impacted files

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##           master    #3720   +/-   ##
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  Coverage   98.42%   98.42%           
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  Files          43       43           
  Lines        5828     5828           
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  Hits         5736     5736           
  Misses         92       92           

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[remi-garcia]

Thanks for the quick commit.

However, this is not consistent anymore with "If the solver doesn't support indicator constraints and the variables do not have a finite domain, you an use the big-M trick."

I believe that something like "If the solver doesn't support indicator constraints, you can use the big-M trick (which requires variables to have a finite domain)." would be better suited.