Add README

- Details core files and dependencies
- Link to test_generator.py for vector generation
- Provide usage instructions for test_runner.py

Author: macgyver13

bip-0375/README.md

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+# BIP 375 Reference Implementation
+
+This directory contains reference implementation for BIP 375: Sending Silent Payments with PSBTs.
+
+## Core Files
+- **`constants.py`** - PSBT field type definitions
+- **`parser.py`** - PSBT structure parsing
+- **`inputs.py`** - Input validation helpers
+- **`dleq.py`** - DLEQ proof validation
+- **`validator.py`** - Main BIP 375 validator
+- **`test_runner.py`** - Test infrastructure (executable)
+
+## Dependencies
+- **`../bip-0374/reference.py`** - BIP 374 DLEQ proof reference
+- **`../bip-0374/secp256k1.py`** - secp256k1 implementation
+
+## Testing
+
+### Test Vectors
+- **`test_vectors.json`** - 17 test vectors (13 invalid + 4 valid) covering:
+  - Invalid input types (P2MS, non-standard scripts)
+  - Missing/invalid DLEQ proofs
+  - ECDH share validation
+  - Output script verification
+  - SIGHASH requirements
+  - BIP-352 output address matching
+
+### Generating Test Vectors
+
+Test vectors were generated using [test_generator.py](https://github.com/macgyver13/bip375-examples/blob/main/python/tests/test_generator.py)
+
+### Run Tests
+
+```bash
+python test_runner.py                    # Run all tests
+python test_runner.py -v                 # Verbose mode with detailed errors
+```
+
+**Expected output:** All 17 tests should pass validation (4 valid accepted, 13 invalid rejected).
+
+## Validation Layers
+
+The validator implements progressive validation:
+1. **PSBT Structure** - Parse PSBT v2 format
+2. **Input Eligibility** - Validate eligible input types (P2PKH, P2WPKH, P2TR, P2SH-P2WPKH)
+3. **DLEQ Proofs** - Verify ECDH share correctness using BIP-374
+4. **Output Fields** - Check PSBT_OUT_SCRIPT or PSBT_OUT_SP_V0_INFO requirements
+5. **BIP-352 Outputs** - Validate output scripts match expected silent payment addresses
+
+## Examples
+
+Demo implementations using this reference can be found in [bip375-examples](https://github.com/macgyver13/bip375-examples/)