Update instructions after the static content asset change

See: https://github.com/apache/incubator-pekko-sbt-paradox/pull/86#issuecomment-1867992884 Depends on: https://github.com/apache/incubator-pekko-sbt-paradox/issues/84

Devs need a way to debug static assets in this repo after the static content asset change.
Either:
- Update instructions for copying static assest fetched from the CDN in https://github.com/apache/incubator-pekko/tree/main/docs/src/main/paradox/_template just for testing purposes
- Prepare a scripts that automate the step above

Start with the discussion in pull request 86 and the dependency issue 84, then inspect docs/src/main/paradox/_template. Determine how static assets are fetched from the CDN and what developers currently need to do for testing; done means documenting that workflow or providing an agreed script to automate it.

Written by the indexing model from the issue text.