Document the Protected Cards feature

[waldyrious]

No description provided.

[fmfmartins]

Do we want to apply the semantic linefeeds pattern to this document as well?

[waldyrious]

Good point! Since it's a new document being added, we should take the opportunity to introduce it from the get-go with the line breaks. Thanks for the reminder, I'll update the PR shortly.

[waldyrious]

@fmfmartins PR updated. I've broken the longest lines in semantically meaningful places. There are still some relatively long lines left, but the structure of those sentences doesn't provide obvious places to break them further. We could improve the situation with additional work in rewording this content, but IMHO that work should be left to a subsequent improvement PR, so we can get this content out there (especially since these breaks aren't visible in the rendered docs anyway).