Add initial set of doc comments to the SDK (#4513)

Also perform minor code cleanup.

sdk/typescript/README.md

@@ -1 +1,53 @@
 # Codex SDK
+
+Bring the power of the best coding agent to your application.
+
+## Installation
+
+```bash
+npm install @openai/codex-sdk
+```
+
+## Usage
+
+Call `startThread()` and `run()` to start a thead with Codex.
+
+```typescript
+import { Codex } from "@openai/codex-sdk";
+
+const codex = new Codex();
+const thread = codex.startThread();
+const result = await thread.run("Diagnose the test failure and propose a fix");
+
+console.log(result);
+```
+
+You can call `run()` again to continue the same thread.
+
+```typescript
+const result = await thread.run("Implement the fix");
+
+console.log(result);
+```
+
+### Streaming
+
+The `await run()` method completes when a thread turn is complete and agent is prepared the final response.
+
+You can thread items while they are being produced by calling `await runStreamed()`.
+
+```typescript
+const result = thread.runStreamed("Diagnose the test failure and propose a fix");
+```
+
+### Resuming a thread
+
+If you don't have the original `Thread` instance to continue the thread, you can resume a thread by calling `resumeThread()` and providing the thread.
+
+```typescript
+const threadId = "...";
+const thread = codex.resumeThread(threadId);
+const result = await thread.run("Implement the fix");
+
+console.log(result);
+```