[docs] update should_i_use.md

[odow]

A few tweaks:

• fix a very poor sentence
• emphasize real and complex value support
• JuMP is no longer special in supporting automatic installation or re-solves

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.38%. Comparing base (a38666a) to head (871d6c2).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3773   +/-   ##
=======================================
  Coverage   98.38%   98.38%           
=======================================
  Files          44       44           
  Lines        5885     5885           
=======================================
  Hits         5790     5790           
  Misses         95       95           

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