docs: add RBTC–USDT0 Cross-Chain Lending Starter Kit documentation

[entuziaz]

Title

Complete documentation guide for the RBTC–USDT0 Lending Boilerplate (https://github.com/rsksmart/rbtc-usdt0-lending-boilerplate).

Description

This PR adds a complete documentation guide for the RBTC–USDT0 Lending Boilerplate. It expands the boilerplate into a cross-chain starter kit by providing:

• A full explanation of the LendingPool, oracle adapter, and USDT0 contracts
• A cross-chain data flow section describing how to extend the boilerplate with LayerZero
• Guidance for replacing the mock Umbrella oracle with real Umbrella/RedStone feeds
• Testnet and local demo instructions
• Use cases and developer extension notes

No contract logic was modified. This PR adds documentation only.
anges.

Testing

N/A

Checklist

• I have read and understood the contributing guidelines.
• I have followed the style guide and formatting guidelines.
• I have added appropriate comments to explain the changes.
• I have tested my changes thoroughly.

Refs

• Code Repo: https://github.com/rsksmart/rbtc-usdt0-lending-boilerplate

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