Hide warning about incompleteness

[kpp]

The red banner with "For now, this reference is a best-effort document..." scares me a lot. Would you please add a button "I got it" which hides the banner and sets a cookie that prevents its popup again?

[ehuss]

I would personally like to just remove it. Or just have it on the front page. @Havvy @Centril do you have an opinion? I added a github link in the upper-right corner of every page, if people want an easy way to file issues.

[Centril]

The warning seems useless atm -- maybe we should exchange it for "this document is not normative".

[ehuss]

The front page already says "Finally, this book is not normative." and includes a big red box that it is incomplete, and emphasizes that it is informal. I don't think it needs shouting on every page.

[Centril]

Oh; that banner. Sure, yeah, let's remove it.