Fix typo.

doc/org.texi

@@ -541,7 +541,7 @@ You need to fix the single quotes by hand, or copy from Info
 documentation.}
 @end iftex
 
-Add the following lines to your @file{.emacs} file.  The last two lines
+Add the following lines to your @file{.emacs} file.  The last three lines
 define @emph{global} keys for the commands @command{org-store-link},
 @command{org-agenda}, and @command{org-iswitchb} - please choose suitable
 keys yourself.