doc/lispref/text.texi(Margins): Add an index.

doc/lispref/ChangeLog

 2013-08-16  Xue Fuqiao  <xfq.free@gmail.com>
 
 	* text.texi (Insertion): Refine.
+	(Margins): Add an index.
 
 	* positions.texi (Character Motion):
 	* markers.texi (Moving Markers):

doc/lispref/text.texi

@@ -484,6 +484,7 @@ it except to install it on a keymap.
 
 In an interactive call, @var{count} is the numeric prefix argument.
 
+@c FIXME: This variable is obsolete since 23.1.
 Self-insertion translates the input character through
 @code{translation-table-for-input}.  @xref{Translation of Characters}.
 
@@ -1613,6 +1614,7 @@ newlines'' act as paragraph separators.
 
 @node Margins
 @section Margins for Filling
+@cindex margins, filling
 
 @defopt fill-prefix
 This buffer-local variable, if non-@code{nil}, specifies a string of