doc: interactive.singleKey is disabled by default

Make it clear that the interactive.singleKey configuration option is
disabled by default, using rather subtle wording that avoids an
emphasis on the actual default value.  This should eliminate any
associated doubts.

While there, touch up the remaining wording of the description a bit.

Signed-off-by: Dragan Simic <dsimic@manjaro.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: Dragan Simic

Documentation/config/interactive.txt

@@ -1,8 +1,8 @@
 interactive.singleKey::
-	In interactive commands, allow the user to provide one-letter
-	input with a single key (i.e., without hitting enter).
-	Currently this is used by the `--patch` mode of
-	linkgit:git-add[1], linkgit:git-checkout[1],
+	When set to true, allow the user to provide one-letter input
+	with a single key (i.e., without hitting the Enter key) in
+	interactive commands.  This is currently used by the `--patch`
+	mode of linkgit:git-add[1], linkgit:git-checkout[1],
 	linkgit:git-restore[1], linkgit:git-commit[1],
 	linkgit:git-reset[1], and linkgit:git-stash[1].