Confusing docs: Command::output claims to "capture" stdin

[crumblingstatue]

By default, stdin, stdout and stderr are captured (and used to provide the resulting output).

"capture" makes it sound like the data is stored somewhere for later inspection. There is no stdin field in process::Output.

I did some looking into the implementation, and to me it seems that the child's stdin is simply closed before waiting. @talchas on IRC told me that it's made to be Stdio::null().

In any case, this should be clarified.

cc @steveklabnik

[frewsxcv]

Opened a pull request for this: #46220