Add meta infos to `eosc` website

[mathboulianne]

Add meta infos to eosc website

• [ ] Add thumbnail
• [ ] Add meta description: The most flexible & powerful command line tool for any developer to interact with an EOSIO chain
• [ ] Add meta keyword: eosc, cleos, keosd, eosio, command line tool, dapp developer, eos mainet, eos vault, eos wallet, multiplatform, EOS referendum, EOS software, EOS voting