create documentation for xss comments

[michael-volynets]

@tomholub please create documentation that describes // xss-... comments because it's hard to understand where and which xss comment a developer should use.

Please describe why we need the xss comments and what every comment means.

Thanks :)

[tomholub]

Here https://github.com/FlowCrypt/flowcrypt-browser/wiki/FlowCrypt-TypeScript-Style-Guide#rendering-untrusted-content

@michael-volynets

[michael-volynets]

Thank you!

[rrrooommmaaa]

I noticed that we use jQuery .after and its not covered by the xss pattern regex. (It covers html|append|prepend|replaceWith|insertBefore|insertAfter and innerHTML|outerHTML)
How critical is this? Should we fix?

[tomholub]

definitely safer to cover it, thank you for noticing