Ask HN: Best solution for encrypting text data, accessible publicly?

I've been buying cryptocurrencies and I'd like to leave instructions for my family to restore them should something happen to me.

They're non-technical so the simpler for them, the better. I was thinking I could just encrypt a text file which is unlockable by a password.

The question is where can I host this data and update it easily as well? Some sort of encrypted git would be ideal. It doesn't have to live online forever, just for the next while until a better solution comes up. I suppose I could just keep an encrypted file on dropbox?