Add index entry for gutter.

I don't do more since a person who knows what a gutter actually is (inner
margin + binding offset) can deduce its value easily.

diff --git a/Documentation/notation/spacing.itely b/Documentation/notation/spacing.itely
index b1afc3b2bb657a9db18d26d7ad48b28cf240d74a..53733649a87d47bdc1376c9b74d37df2dbc36ce7 100644 (file)
--- a/Documentation/notation/spacing.itely
+++ b/Documentation/notation/spacing.itely
@@ -728,6 +728,9 @@ Default: unset.
 @item two-sided
 @funindex two-sided
 
+@cindex gutter
+@cindex binding gutter
+
 If set to true, use @code{inner-margin}, @code{outer-margin} and
 @code{binding-offset} to determine margins depending on whether
 the page number is odd or even.  This overrides @code{left-margin}