Add smart contract programming

[dbosk]

Based on some coverage of DLTs, add smart contract programming.

There are several options:

• Ethereum's Solidity language, there is also this material by Bonneau from the FOSAD summer school.
• Ethereum also has Vyper, which is a Python-like language for writing smart contracts.
• Dfinity might have something useful too. Or maybe it's still too early.