Add default yandex CSP to readme.md

[rempash]

Hi
We usually work with angular in the enterprise environment, and most of the time we need CSP to make requests and get resources for external libraries. Maybe I can add an example of CSP for yandex-maps, because some URLs cannot be found in their documentation, so users of this library can just copy the CSP string and add it to their project.

[ddubrava]

Hi! You can create a repro on stackblitz, I'll fork it and send you a link, then you can raise a PR.
Or any other ideas?