Fix outdated output redirection docs (#2200)

The 0.92.0 release notes document the behavior previously documented here.

Update to current behavior.

The 0.92.0 release notes

> File redirections (`o>`, `e>`, `o+e>`, etc.) now apply to all ***external*** commands inside an expression.

I searched this repository for ` e> `, ` o> `, ` err> `, ` out> `, `subexpression`, `piping`. I was not able to identify release notes that document changed behavior after 0.92.0, and checked the [0.92.0 PR](nushell/nushell#11934) for linked followups or comments.

Resolves #2152
Resolves nushell/nushell#17604

Author: Kissaki

book/stdout_stderr_exit_codes.md

@@ -99,12 +99,23 @@ use std
 cat unknown.txt o+e> (std null-device)
 ```
 
-Note that file redirections are scoped to an expression and apply to all external commands in the expression. In the example below, `out.txt` will contain `hello\nworld`:
+Semicolons follow defined pipeline behavior. In the following example, the first expression prints to stdout, and the second becomes the result of the parentheses-subexpression and gets piped into `out.txt`.
 ```nu
 let text = "hello\nworld"
 ($text | head -n 1; $text | tail -n 1) o> out.txt
+# => hello
+open out.txt
+# => world
+```
+
+To combine the output, scope them into a block and execute it with `do`:
+```nu
+let text = "hello\nworld"
+do { $text | head -n 1; $text | tail -n 1 } o> out.txt
+open out.txt
+# => hello
+# => world
 ```
-Pipes and additional file redirections inside the expression will override any file redirections applied from the outside.
 
 ## Pipe Redirections