README: Add Text-To-Speech example

[mauriciovasquezbernal]

Describe the change
Add example of Test-To-Speech API

Provide OpenAI documentation link
N/A

Describe your solution
N/A

Tests
N/A

Additional context
N/A

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.44%. Comparing base (a09cb0c) to head (d34a482).
Report is 74 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #617   +/-   ##
=======================================
  Coverage   98.44%   98.44%           
=======================================
  Files          24       24           
  Lines        1354     1354           
=======================================
  Hits         1333     1333           
  Misses         15       15           
  Partials        6        6           

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