Expand README with more info from the docc bundle (#3)

Expand README with more info from the docc bundle

## Summary

Copied a subset of the information on the landing page of the docc bundle into the README.

## Test Plan

Previewed locally, looks good.


Reviewed by: simonjbeaumont

Builds:
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     ✔︎ pull request validation (5.9) - Build finished. 
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#3

Author: czechboy0

README.md

@@ -1,9 +1,52 @@
 # Swift OpenAPI Generator Runtime
 
-This library provides common abstractions and helper functions used by all
-client and server code generated by [Swift OpenAPI Generator][0].
+This library provides common abstractions and helper functions used by the client and server code generated by [Swift OpenAPI Generator][0].
 
-To get started, check out the [documentation][1].
+## Overview
+
+It contains:
+- Common types used in the code generated by the `swift-openapi-generator` package plugin.
+- Protocol definitions for pluggable layers, including `ClientTransport`, `ServerTransport`, and middleware.
+
+## Usage
+
+Add the package dependency in your `Package.swift`:
+
+```swift
+.package(url: "https://github.com/apple/swift-openapi-runtime", from: "0.1.0"),
+```
+
+and in your target, add `OpenAPIRuntime` to your dependencies:
+
+```swift
+.target(name: "MyTarget", dependencies: [
+    .product(name: "OpenAPIRuntime", package: "swift-openapi-runtime"),
+],
+```
+
+The next step depends on your use case.
+
+### Using Swift OpenAPI Generator for code generation
+
+The generated code depends on types from this library. Check out the adoption guides in the [Swift OpenAPI Generator documentation][1] to see how the packages fit together.
+
+### Implementing transports and middlewares
+
+Swift OpenAPI Generator generates client and server code that is designed to be used with pluggable transports and middlewares.
+
+Implement a new transport or middleware by providing a type that adopts one of the protocols from the runtime library:
+
+* `ClientTransport`
+* `ClientMiddleware`
+* `ServerTransport`
+* `ServerMiddleware`
+
+You can also publish your transport or middleware as a Swift package to allow others to use it with their generated code.
+
+## Documentation
+
+To learn more, check out the full [documentation][2].
 
 [0]: https://github.com/apple/swift-openapi-generator
 [1]: https://swiftpackageindex.com/apple/swift-openapi-generator/documentation
+[2]: https://swiftpackageindex.com/apple/swift-openapi-runtime/documentation

Sources/OpenAPIRuntime/Documentation.docc/Documentation.md

@@ -4,13 +4,46 @@ Use and extend your client and server code generated by Swift OpenAPI Generato
 
 ## Overview
 
+This library provides common abstractions and helper functions used by the client and server code generated by [Swift OpenAPI Generator][0].
 
-This library provides common abstractions and helper functions used by all client and server code generated by [Swift OpenAPI Generator][0].
+It contains:
+- Common types used in the code generated by the `swift-openapi-generator` package plugin.
+- Protocol definitions for pluggable layers, including ``ClientTransport``, ``ServerTransport``, and middleware.
 
-### Supported Use Cases
+### Usage
 
-1. Use the types from this library to instantiate your generated client and server code. To learn more, review the adoption guides in the [Swift OpenAPI Generator documentation][1].
-2. Implement a custom transport or middleware to extend your generated client and server. For client code, check out ``ClientTransport`` and ``ClientMiddleware``. For server code, check out ``ServerTransport`` and ``ServerMiddleware``.
+Add the package dependency in your `Package.swift`:
+
+```swift
+.package(url: "https://github.com/apple/swift-openapi-runtime", from: "0.1.0"),
+```
+
+and in your target, add `OpenAPIRuntime` to your dependencies:
+
+```swift
+.target(name: "MyTarget", dependencies: [
+    .product(name: "OpenAPIRuntime", package: "swift-openapi-runtime"),
+],
+```
+
+The next step depends on your use case.
+
+#### Using Swift OpenAPI Generator for code generation
+
+The generated code depends on types from this library. Check out the adoption guides in the [Swift OpenAPI Generator documentation][1] to see how the packages fit together.
+
+#### Implementing transports and middlewares
+
+Swift OpenAPI Generator generates client and server code that is designed to be used with pluggable transports and middlewares.
+
+Implement a new transport or middleware by providing a type that adopts one of the protocols from the runtime library:
+
+* ``ClientTransport``
+* ``ClientMiddleware``
+* ``ServerTransport``
+* ``ServerMiddleware``
+
+You can also publish your transport or middleware as a Swift package to allow others to use it with their generated code.
 
 ## Topics