Update 'Smart Contracts on Ethereum, Bitcoin and Bitcoin Cash.' article

[mr-zwets]

the article 'Smart Contracts on Ethereum, Bitcoin and Bitcoin Cash.' was written in 2019 and is linked in the readme

we might want to take the time to update it sometime

[rkalis]

For the short term, maybe it's best to remove the link from the readme since it's already quite outdated. Then we can consider to update the article / publish a new article on the CashScript docs in the future.