Suggestion. Task for 'Iterables' article

还没有人认领这个 Issue。

It would be useful to have some practice tasks with realization of concepts in article [Iterables](https://javascript.info/iterable).

An idea of task is in the article: "make an iterable object that generates an infinite sequence of pseudorandom numbers".

Possible solution:
```
let randomObj = {
min: 10,
max: 100,
}

randomObj[Symbol.iterator] = function() {
return {
start: this.min,
end: this.max,
next() {
return {
done: false,
value: Math.random() * (this.end - this.start) + this.start,
};
}
}
}

const THRESHOLD = 20;

for (let value of randomObj) {
alert(value); // show random generated value
if (value < THRESHOLD) break;
}
````

首先阅读链接的 Iterables 文章及其现有的练习结构。以提议的无限伪随机数 iterable 作为任务参考，然后检查教程其他部分是如何组织实践任务的。完成的标准是：文章包含一个适当的实践任务，并提供清晰的题目说明和解决方案指导。

由索引模型根据 Issue 内容生成。