config.txt: clarify multiple key values in include.path

The phrasing in this paragraph may give an impression that you can only
use it once. Rephrase it a bit.

Helped-by: Philip Oakley <philipoakley@iee.org>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -79,10 +79,10 @@ escape sequences) are invalid.
 Includes
 ~~~~~~~~
 
-You can include one config file from another by setting the special
+You can include a config file from another by setting the special
 `include.path` variable to the name of the file to be included. The
 variable takes a pathname as its value, and is subject to tilde
-expansion.
+expansion. `include.path` can be given multiple times.
 
 The
 included file is expanded immediately, as if its contents had been