Fix broken internal links in reference implementation

- Add index.md files for directory navigation in Jekyll build
- Fix LICENSE reference: change from missing file to CC0 statement
- Fix broken EIP-walkthrough.md link: replace with ERC-7963 spec URL
- Update resource links and capitalize Payment Instruction properly

Author: chadxeth

assets/erc-7963/eip-permissioned-erc20/README.md

@@ -162,4 +162,4 @@ This project has been migrated from Circom to RISC Zero for improved performance
 
 ## License
 
-This project is licensed under the MIT License - see the [LICENSE](LICENSE) file for details.
+This reference implementation is part of ERC-7963 and is released under CC0 (public domain).

assets/erc-7963/eip-permissioned-erc20/index.md

@@ -0,0 +1,20 @@
+# ERC-7963 Reference Implementation
+
+This directory contains the complete reference implementation for ERC-7963: Oracle-Permissioned ERC-20 with ZK Proofs.
+
+## Contents
+
+- **[README.md](README.md)** - Full documentation, setup instructions, and usage guide
+- **[contracts/](contracts/)** - Solidity smart contracts (ERC-20, Oracle, Verifier)
+- **[zk/](zk/)** - RISC Zero guest programs for ZK proof generation
+- **[test/](test/)** - Comprehensive test suite (Hardhat/TypeScript)
+- **[scripts/](scripts/)** - Deployment and utility scripts
+- **[examples/](examples/)** - Example usage and demos
+
+## Quick Start
+
+See [README.md](README.md) for detailed setup and installation instructions.
+
+## License
+
+This reference implementation is part of ERC-7963 and is released under CC0 (public domain).

assets/erc-7963/eip-permissioned-erc20/zk/README.md

@@ -354,5 +354,5 @@ When modifying the guest program:
 
 - [RISC Zero Documentation](https://dev.risczero.com/)
 - [RISC Zero Examples](https://github.com/risc0/risc0/tree/main/examples)
-- [payment instruction Specification](https://www.iso20022.org/)
-- [EIP Permissioned ERC-20 Documentation](../docs/EIP-walkthrough.md)
+- [Payment Instruction Specification](https://www.iso20022.org/)
+- [ERC-7963 Specification](https://eips.ethereum.org/EIPS/eip-7963)

assets/erc-7963/eip-permissioned-erc20/zk/index.md

@@ -0,0 +1,19 @@
+# ERC-7963 ZK Programs
+
+This directory contains the RISC Zero guest programs and host utilities for generating zero-knowledge proofs for ERC-7963.
+
+## Contents
+
+- **[README.md](README.md)** - Detailed documentation for the ZK programs
+- **[methods/](methods/)** - RISC Zero guest program implementations
+- **[host/](host/)** - Host program for proof generation
+- **[test-utils/](test-utils/)** - Testing utilities and data generators
+
+## Quick Start
+
+See [README.md](README.md) for setup instructions and usage examples.
+
+## Resources
+
+- [RISC Zero Documentation](https://dev.risczero.com/)
+- [ERC-7963 Specification](https://eips.ethereum.org/EIPS/eip-7963)