feat(core): add sample app

[GroovinChip]

Also update the code in the readme

• I have signed the Stream CLA (required).
• The code changes follow best practices
• Code changes are tested (add some information if not applicable)

Description of the pull request

[codecov]

Codecov Report

Merging #170 (a51f951) into support-extraData-null-value (6743455) will not change coverage.
The diff coverage is n/a.

❗ Current head a51f951 differs from pull request most recent head 12566ba. Consider uploading reports for the commit 12566ba to get more accurate results

@@                      Coverage Diff                      @@
##           support-extraData-null-value     #170   +/-   ##
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  Coverage                         76.38%   76.38%           
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  Files                                87       87           
  Lines                              2638     2638           
=============================================================
  Hits                               2015     2015           
  Misses                              623      623           

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