Document the color.interactive semantics

There are two possible confusions with the color.interactive
description:

  1. the short name "interactive" implies that it covers all
     interactive commands; let's explicitly make it so, even
     though there are no other interactive commands which
     currently use it

  2. Not all parts of "git add --interactive" are controlled
     by color.interactive (specifically, the diffs require
     tweaking color.diff). So let's clarify that it applies
     only to displays and prompts.

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

Documentation/config.txt

diff --git a/Documentation/config.txt b/Documentation/config.txt
index d44bc7a..1a90e6b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -406,7 +406,8 @@
 	in color.branch.<slot>.
 
 color.interactive::
-	When set to `always`, always use colors in `git add --interactive`.
+	When set to `always`, always use colors for interactive prompts
+	and displays (such as those used by "git add --interactive").
 	When false (or `never`), never.  When set to `true` or `auto`, use
 	colors only when the output is to the terminal. Defaults to false.