[pitivi] help: update the Timeline section in mainwindow.page

[Jean-François Fortin Tam <jfft src gnome org>]

commit 1052599b2e3c6feb012abb56676feb8a2db5ac96
Author: Tomas Karger <tomkarger gmail com>
Date:   Fri Jan 31 16:44:19 2014 +0100

    help: update the Timeline section in mainwindow.page

 help/C/mainwindow.page |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/help/C/mainwindow.page b/help/C/mainwindow.page
index 20cde35..a739105 100644
--- a/help/C/mainwindow.page
+++ b/help/C/mainwindow.page
@@ -70,7 +70,8 @@
 
     <section>
      <title>Timeline</title>
-      <p>The timeline is the core user interface component that you will use for editing. It is a visual, 
time-proportional representation of your project's chronology.</p>
+      <p>The timeline is the core user interface component that you will use for editing. Vertically, it is 
divided into layers that can be filled with audio and video clips. Horizontally, it constitutes a 
time-proportional representation of your project's chronology. Various levels of zoom can be applied to the 
timeline. However, these apply only to the horizontal (chronological) dimension of the timeline.</p>
+      <p>See the <link xref="layers">Understanding layers</link> and <link xref="movearoundtimeline">Moving 
around the timeline</link> pages for more information on how to work with the timeline.</p>
     </section>
 
     <section>