Revise sentence regarding async (#102)

Current sentence is confusing, so I fixed it.

Author: PPPDUD

docs/development/extensions/async.md

@@ -6,7 +6,7 @@ hide_table_of_contents: true
 
 import {ExtensionCode} from './utils.js';
 
-Sometimes you will want your extension to wait for an "asynchronous" or "async" operation to complete before resuming instead of for your block to complete (almost) immediately. A common example of this is making a request: no matter how fast your internet is, any network request is not going to be instant.
+Sometimes you will want your extension to wait for an "asynchronous" or "async" operation to complete before resuming execution (versus resuming execution early and potentially causing problems). A common example of this is making a request: no matter how fast your internet is, any network request is not going to be instant.
 
 Modern JavaScript has a cool utility for dealing with these: [Promises](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise). These are how your block can inform Scratch that your block is waiting for an async operation to complete, and the eventual value.