add READMEs for each package

Author: shirakaba

packages/ios/README.md

@@ -0,0 +1,19 @@
+# @nativescript/ios-node-api
+
+An embeddable, engine-agnostic NativeScript runtime for iOS based on Node-API.
+
+## Installation
+
+These steps assume that you're making an iOS app that includes a Node-API-capable JavaScript runtime and manages its JS dependencies using npm (or similar package managers).
+
+First, install the npm package:
+
+```sh
+npm install @nativescript/ios-node-api
+```
+
+Next, embed the xcframework provided at `build/ios-universal/NativeScript.xcframework` into your iOS app. For convenience, we provide `NativeScript.podspec` so that you can link it as a local podspec. For React Native (or Expo) apps, this will be autolinked.
+
+## Usage
+
+Until we have some example projects to provide, a few example usages in an Expo app are shown in this [tweet](https://x.com/birch_js/status/1773401773266604240).

packages/macos/README.md

@@ -0,0 +1,13 @@
+# @nativescript/macos-node-api
+
+An embeddable, engine-agnostic NativeScript runtime for macOS based on Node-API.
+
+## Installation
+
+```sh
+npm install @nativescript/macos-node-api
+```
+
+## Usage
+
+See [examples](https://github.com/DjDeveloperr/runtime/tree/main/examples) in the repo. Best run on Node.js for now.

packages/objc/README.md

@@ -0,0 +1,5 @@
+# @nativescript/objc-node-api
+
+Typings for the common Objective-C runtime APIs used by both `@nativescript/ios-node-api` and `@nativescript/macos-node-api`.
+
+This is intended to be used as a subdependency of the aforementioned packages, so please consult their documentation.