Update wording on appending standard output

Clarify the explanation regarding appending standard output.

Author: TropicolX

stage_descriptions/redirection-03-el9.md

@@ -15,7 +15,7 @@ first
 second
 ```
 
-You can also explicitly write `1>>` to append to standard output. Both `>>` and `1>>` do exactly the same thing.
+You can also explicitly write `1>>` to append the command's standard output to a file. Both `>>` and `1>>` do exactly the same thing.
 
 ### Tests