fixing link to use cases readme

[silviabotros]

Short description of what this PR does:

Fixing the link to use cases markdown file in the README and TROUBLESHOOTING guide

[SendGridDX]

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[codecov]

Codecov Report

Merging #581 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #581   +/-   ##
=======================================
  Coverage   86.77%   86.77%           
=======================================
  Files          32       32           
  Lines         983      983           
  Branches      127      127           
=======================================
  Hits          853      853           
  Misses         67       67           
  Partials       63       63

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[thinkingserious]

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