use top-level await (#98)

Author: Mohamed Nainar

content/welcome.mdx

@@ -37,14 +37,11 @@ This is the simplest possible way to connect, query, and disconnect with async/a
 ```js
 const { Client } = require('pg')
 const client = new Client()
+await client.connect()
 
-;(async () => {
-  await client.connect()
-
-  const res = await client.query('SELECT $1::text as message', ['Hello world!'])
-  console.log(res.rows[0].message) // Hello world!
-  await client.end()
-})()
+const res = await client.query('SELECT $1::text as message', ['Hello world!'])
+console.log(res.rows[0].message) // Hello world!
+await client.end()
 ```
 
 And here's the same thing with callbacks: