fix(learn): improve the learn Asynchronous Work doc

apps/site/pages/en/learn/asynchronous-work/understanding-processnexttick.md

@@ -31,25 +31,27 @@ Use `nextTick()` when you want to make sure that in the next event loop iteratio
 console.log('Hello => number 1');
 
 setImmediate(() => {
-  console.log('Running before the timeout => number 3');
+  console.log('Running at order 3 or 4, setImmediate');
 });
 
 setTimeout(() => {
-  console.log('The timeout running last => number 4');
+  console.log('Running at order 3 or 4, setTimeout');
 }, 0);
 
 process.nextTick(() => {
   console.log('Running at next tick => number 2');
 });
 ```
 
-#### Example output:
+#### Example output(possible):
 
 ```bash
 Hello => number 1
 Running at next tick => number 2
-Running before the timeout => number 3
-The timeout running last => number 4
+Running at order 3 or 4, setImmediate
+Running at order 3 or 4, setTimeout
 ```
 
-The exact output may differ from run to run.
+In that case, `console.log('Hello => number 1');` will first run because event loop only starts after call stack is cleared.The `nextTick` queue is processed before entering the next phase, which is why the `process.nextTick()` callback runs immediately after.
+
+The execution order of `serImmediate` and `setTimeout` can not be determined in the main module. For a detailed explanation, refer to [setImmediate vs setTimeout](https://nodejs.org/en/learn/asynchronous-work/event-loop-timers-and-nexttick#setimmediate-vs-settimeout).