docs: add ELI5 video to home page

[dmitryvinn-fb]

Summary

Here at Meta Open Source, we've been creating short-form videos to explain Meta OSS projects in the simplest terms possible. We started embedding these videos into project pages as you can see in Hermes home pageor in Docusaurus home page](https://docusaurus.io/)

Test plan

This is how the video appears on the home page:

[codecov-commenter]

Codecov Report

Merging #12379 (a501c2c) into main (faef0b4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main   #12379   +/-   ##
=======================================
  Coverage   68.47%   68.47%           
=======================================
  Files         324      324           
  Lines       16967    16967           
  Branches     5060     5060           
=======================================
  Hits        11618    11618           
  Misses       5317     5317           
  Partials       32       32           

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[Biki-das]

@dmitryvinn-fb that's a good one, please run yarn lint:prettier and push again , this should solve the failed lint check.

[SimenB]

thanks!

[dmitryvinn-fb]

Thank you all!

[github-actions]

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