Update instructions after the static content asset change

[samueleresca]

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