Base: Mention -n option in echo(1) manpage

Author: https://github.com/linusg
Commit: 1002236715
Pull-request: https://github.com/SerenityOS/serenity/pull/5427

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

@@ -5,7 +5,7 @@ echo - print the given text
 ## Synopsis
 
 ```**sh
-$ echo text...
+$ echo [-n] text...
 ```
 
 ## Description
@@ -13,6 +13,10 @@ $ echo text...
 Print the given *text*, which is passed as argv, to the standard output,
 separating arguments with a space character.
 
+## Options
+
+* `-n`: Do not output a trailing newline
+
 ## Examples
 
 ```sh