Add page about Catchain

[ilyar]

Add page about Catchain

Reference

• https://habr.com/ru/company/mercuryo/blog/490392/
• https://docs.ton.dev/86757ecb2/p/07ddda-walk-through-the-catchain/t/43bd4e
• https://www.google.com/search?q=Catchain
• https://github.com/tonlabs/ton-labs-node/blob/master/catchain/README.md
• https://everscale-community.medium.com/walkthrough-the-catchain-6fb4d25b1d3

[ilyar]

https://docs.everscale.network/arch/consensus/messages