rev: Document the '-' filename

Author: https://github.com/Mango0x45
Commit: 5a4ee4df34
Pull-request: https://github.com/SerenityOS/serenity/pull/15381
Reviewed-by: https://github.com/MacDue ✅

Base/usr/share/man/man1/rev.md

@@ -5,14 +5,19 @@ rev - reverse lines
 ## Synopsis
 
 ```*sh
-$ rev [files...]
+$ rev [file...]
 ```
 
 ## Description
 
 `rev` reads the specified files line by line, and prints them to standard
 output with each line being reversed characterwise. If no files are specified,
-then `rev` will read from standard input.
+then `rev` will read from standard input. If the file `-` is specified then
+`rev` also reads from standard input.
+
+## Arguments
+
+* `file`: Files to print
 
 ## Examples
 
@@ -39,3 +44,18 @@ $ ls | rev
 oof
 rab
 ```
+
+To print a file 'foo' in reverse followed by the output of `ls` in reverse:
+```sh
+$ cat foo
+foo 1
+foo 2
+$ ls
+foo
+bar
+$ ls | rev foo -
+1 oof
+2 oof
+oof
+rab
+```