翻译错误：2.1.1

[Michael Johnson]

原文如下：
This is about as simple as it gets. Of course, you have to make sure that the
header is included so the compiler can see the definition of the std::thread class. As
with much of the C++ Standard Library, std::thread works with any callable type, so
you can pass an instance of a class with a function call operator to the std::thread
constructor instead:

译文如下：
为了让编译器识别std::thread类，这个简单的例子也要包含头文件。如同大多数C++标准库一样，std::thread可以用可调用类型构造，将带有函数调用符类型的实例传入std::thread类中，替换默认的构造函数。

错误位置：
so you can pass an instance of a class with a function call operator to the std::thread
constructor instead
这里指的并不是替换默认构造函数，这个instead指的是用类实例的函数调用运算符替换普通的函数，就是前面定义的do_some_work函数。

[xiaowei]

这里的翻译确实有偏差。
不过，an instance of a class with a function call operator指得并不是do_some_work函数，而是下面具有函数操作符的background_task类。

[Michael Johnson]

我指的是instead的东西，他是要替换的do_some_work，用an instance of a class with a function call operator来instead掉do_some_work

[xiaowei]

ok，那明白了。修改后的翻译，和你的意思应该是等价的。