Add hint about generating hash

[php-coder]

It would be great to provide a simple instruction that people can use for generating sha256 for their code. For example:

$ echo -n 'box-shadow: none; border: 0px;' | openssl dgst -sha256 -binary | base64

[php-coder]

Or at least add this link: https://www.owasp.org/index.php/Content_Security_Policy_Cheat_Sheet#Refactoring_inline_code

[pfreitag]

Fixed in 668d9ea see: https://content-security-policy.com/hash/