Standardize QR code for the address

[maciejhirsz]

Hey there, we are all really impressed by what you've put together here!

While there isn't yet an equivalent of EIP-681, I think it's sensible to anticipate a similar format to emerge in the future. Therefore I'd propose to include a substrate: URI scheme in the QR code with the address that you show:

substrate:5GKhf...tmx

I'll propose the same for Substrate part of Universal Offline Signatures.

[0xthreebody]

@maciejhirsz Thanks for your guidance. I'll study the problem carefully.