Documentation: Document CSP recommendations

[karlhorky]

Hi, I was just trying to use Sandpack (via @codesandbox/sandpack-react) with an app with a strict Content Security Policy (CSP) today, and I couldn't find any CSP documentation.

Maybe it would make sense to document the recommendations for CSP?

Eg:

frame-src https://*.codesandbox.io/

This would cover the https://2-14-4-sandpack.codesandbox.io/ format that I saw was being requested as a frame-src when I was using Sandpack. (apparently this 2-14-4 is the version number of my local package 😮)

I'm not sure if there are any other requirements for a CSP for Sandpack.