config: document --type=color output is a complete line

Even though the newer "--type=color" option to "git config" is meant
to be upward compatible with the traditional "--get-color" option,
unlike the latter, its output is not an incomplete line that lack
the LF at the end.  That makes it consistent with output of other
types like "git config --type=bool".

Document it, as it sometimes surprises unsuspecting users.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-config.txt

@@ -240,7 +240,9 @@ Valid `<type>`'s include:
 	output.  The optional `default` parameter is used instead, if
 	there is no color configured for `name`.
 +
-`--type=color [--default=<default>]` is preferred over `--get-color`.
+`--type=color [--default=<default>]` is preferred over `--get-color`
+(but note that `--get-color` will omit the trailing newline printed by
+`--type=color`).
 
 -e::
 --edit::