Add tutorial on how to get json interface from solidity project

[Sporarum]

Right now we briefly mention json interfaces in the docs, but we never specify neither its structure, nor how to get one
We should fix this and add examples

References:
https://docs.vyperlang.org/en/latest/interfaces.html#implementing-an-interface
https://docs.vyperlang.org/en/latest/structure-of-a-contract.html#imports-via-import