Update Typescript-Example in Usage-Docs (#255)

Author: bastiankoetsier

docs/usage.md

@@ -167,7 +167,12 @@ import { spawn, Thread, Worker } from "threads"
 import { Counter } from "./workers/counter"
 
 const counter = await spawn<Counter>(new Worker("./workers/counter"))
+console.log(`Initial counter: ${await counter.getCount()}`)
+
 await counter.increment()
+console.log(`Updated counter: ${await counter.getCount()}`)
+
+await Thread.terminate(counter)
 ```
 
 ```ts