Update README.md

Author: ksen0

README.md

@@ -95,8 +95,11 @@ async function setup() {
 
 If it takes a while to load the image, the sketch will be "paused" on the line `img = await loadImage('/assets/bricks.jpg');` - once the image is loaded, it will resume.
 
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 ## …using registerPreloadMethod in a addon or library
 
+Under to hood, returns a **Promise** from each loadImage, loadSound, and similar functions. Promises are widely used in JavaScript, so it is possible to use a callback in p5.js 1.x to create a Promise, but p5.js 1.x doesn't expect promises to be used, so you have to ensure yourself that, for example, your draw function doesn't start running before loading is done. For an example of a Promise using a call back, check out the example below that makes p5.sound.js compatible with both 1.x and 2.0:
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 If your addon built with p5.js 1.x uses `registerPreloadMethod` such as in this example from [p5.sound.js](https://github.com/processing/p5.sound.js):
 
 ```js