Register finish listener in createWriteStream example earlier

Author: lejeunerenard

README.md

@@ -286,11 +286,13 @@ Make a write stream to append chunks as blocks.
 ``` js
 const ws = core.createWriteStream()
 
+// Listen for stream finishing
+const done = new Promise(resolve => ws.on('finish', resolve))
+
 for (const data of ['hello', 'world']) ws.write(data)
 ws.end()
 
-// Wait for stream to finish
-await new Promise(resolve => ws.on('finish', resolve))
+await done
 
 console.log(await core.get(core.length - 2)) // 'hello'
 console.log(await core.get(core.length - 1)) // 'world'