Adds information to redirect_std* inline docs

[nishtha981]

Partially addresses issue #35959

Adds examples for redirecting std to a file to the markdown file

[Seelengrab]

This does not redirect stdout in code following this, that already uses the stdout variable internally. It's just rebinding the variable here. Redirecting stdout to a file is done like so:

open("output.txt", "w") do f
redirect_stdout(f) do
    # your code here
end
end

[stevengj]

Moreover, redirect_stdout also redirects standard output from things like C libraries that don't use the Julia stdout variable.

[Seelengrab]

The changes here only partially address #35959 - the majority of the issue, about the current documentation being confusing for people not already familiar with pipes, TTY, streams, C-stdout.. is not clarified here.