Revise README architecture and usage instructions (#4)

Co-authored-by: stringintech <stringintech@gmail.com>

Author: janb84

README.md

@@ -14,11 +14,11 @@ The framework ensures that all language bindings (Go, Python, Rust, etc.) behave
 ## Architecture
 
 ```
-┌─────────────┐         ┌──────────────────┐
-│ Test Runner │────────▶│  Handler Binary  │
-│  (Go CLI)   │ stdin   │  (Go/Rust/etc)   │
-│             │◀────────│                  │
-└─────────────┘ stdout  └──────────────────┘
+┌─────────────┐         ┌───────────────────┐
+│ Test Runner │────────▶│  Handler Binary** │
+│  (Go CLI)   │ stdin   │  (Go/Rust/etc)    │
+│             │◀────────│                   │
+└─────────────┘ stdout  └───────────────────┘
        │                         │
        │                         │
        ▼                         ▼
@@ -35,19 +35,33 @@ The framework ensures that all language bindings (Go, Python, Rust, etc.) behave
 3. [**Test Cases**](./testdata): JSON files defining requests and expected responses
 4. [**Mock Handler**](./cmd/mock-handler/main.go): Validates the runner by echoing expected responses from test cases
 
-**Handler binaries** are not hosted in this repository. They must be implemented separately following the [**Handler Specification**](./docs/handler-spec.md) and should:
+** **Handler binaries** are not hosted in this repository. They must be implemented separately following the [**Handler Specification**](./docs/handler-spec.md) and should:
 - Implement the JSON protocol for communication with the test runner
 - Call the binding API to execute operations
 - Pin to a specific version/tag of this test repository
 
 ## Getting Started
 
-Build and test against the mock handler:
+### Testing Your Binding (Custom Handler)
+
+Test your handler implementation using the test runner:
+
+```bash
+# Build the test runner
+make runner
+
+# Run the test runner against your handler binary
+./build/runner --handler <path-to-your-handler>
+```
+
+### Testing the Runner
+
+Build and test the runner using the mock handler:
 
 ```bash
 # Build both runner and mock handler
 make build
 
-# Run tests against the mock handler
+# Run the test runner against the mock handler
 make test
 ```