Update to README.md to include Hedera Hashgraph

[bmgentile]

Adding Hedera Hashgraph as a PoS network that can issue native NFTs:

• Hedera Token Service (https://www.hedera.com/token-service) for native NFT issuance; this is more energy-efficient than using a smart contract, especially on Ethereum but for any other public or private blockchain framework.
• Emerging sustainability applications are building on Hedera: DOVU (https://hedera.com/users/dovu), Power Transition (https://hedera.com/users/power-transition), RECDeFi (https://recdefi.com/), SEUN (https://seunwater.io/), and many more.

[bmgentile]

Hi team, is anyone able to help merge this pull request? @memo

[memo]

Thanks!

[bmgentile]

Thanks so much @memo !