[jdjioe5-cpu]

Closes #3

Summary of Changes

• Added a dedicated Unbacked yield limitation (Testnet simulation only) section to \contracts/yield_vault/README.md.
• Documented the underlying backing invariant: underlying asset token balance held equals deposited \principal, while accounted \ otal_assets\ equals \principal + accrued.
• Clarified that this behavior is strictly a TESTNET SIMULATION ONLY and not real Treasury Bill/RWA yield.
• Explained why a full share redemption (
  edeem(all_shares)) reverts with \NoLiquidity\ (error code 10) once yield has accrued, noting that this is an expected artifact of the simulation rather than a bug.
• Reaffirmed that user principal deposits remain fully backed and redeemable up to liquid assets.
• Clarified why nominal \share_price\ is optimistic and directed readers to \�vailable_liquidity\ and \max_redeemable\ for honest settlement ceilings.
• Linked directly to \docs/deployment/testnet.md#phase-1-limitations\ for empirical Testnet observations.