Update installation.md to use USE_DJANGO_JQUERY instead of JQUERY_URL

[markddavidoff]

JQUERY_URL=True did not work for me. See https://stackoverflow.com/questions/61727169/django-smart-selects-not-working-properly

[codecov]

Codecov Report

Merging #352 (760885f) into master (699426b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #352   +/-   ##
=======================================
  Coverage   80.46%   80.46%           
=======================================
  Files           8        8           
  Lines         471      471           
  Branches       68       68           
=======================================
  Hits          379      379           
  Misses         60       60           
  Partials       32       32           

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