docs(core): update watch command with new example and embed YT video

[juristr]

Updates: https://nx-dev-git-docs-watch-command-update-nrwl.vercel.app/recipes/running-tasks/workspace-watching

• embedding video
• adding a new use case which is shown in the video in particular and which is most probably the most common one (might be worth emphasizing it more rather than at the end of the page..🤔)

[vercel]

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Name	Status	Preview	Updated (UTC)
nx-dev	✅ Ready (Inspect)	Visit Preview	Sep 16, 2024 9:32am

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