Added sorted set example.

[simonprickett]

Adds a Sorted Set example - how to use ZADD came up as a question in community Discord and I created this example to demonstrate how it works.

[codecov-commenter]

Codecov Report

Merging #2005 (82225d4) into master (00b58e8) will not change coverage.
The diff coverage is n/a.

❗ Current head 82225d4 differs from pull request most recent head c93ea7e. Consider uploading reports for the commit c93ea7e to get more accurate results

@@           Coverage Diff           @@
##           master    #2005   +/-   ##
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  Coverage   94.94%   94.94%           
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  Files         358      358           
  Lines        3343     3343           
  Branches      409      409           
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  Hits         3174     3174           
  Misses         85       85           
  Partials       84       84           

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