[totem/wip/hadess/more-user-docs: 7/8] help: Explain the difference between builtin and external subtitles

[Bastien Nocera <hadess src gnome org>]

commit aee66c20df581cce9a1b2d3ccf6b06ed1f07950d
Author: Bastien Nocera <hadess hadess net>
Date:   Fri Feb 1 12:45:18 2019 +0100

    help: Explain the difference between builtin and external subtitles
    
    Closes: #292

 help/C/subtitles.page | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)
---
diff --git a/help/C/subtitles.page b/help/C/subtitles.page
index 8043885c0..2a896eb29 100644
--- a/help/C/subtitles.page
+++ b/help/C/subtitles.page
@@ -24,11 +24,22 @@
   <title>Subtitles</title>
 
   <p>
-  <app>Videos</app> loads subtitles automatically if <gui>Load subtitle files
-  when movie is loaded</gui> is enabled in the 
+  Depending on the video format, subtitles can be built into the video file or
+  disc itself, or available as external files.
+  </p>
+
+  <p>
+  To select which subtitle to use when the video file, or disc, contains subtitles,
+  choose press the menu button in the top-right corner of the window and select
+  <guiseq><gui style="menuitem">Subtitles</gui></guiseq>.
+  </p>
+
+  <p>
+  <app>Videos</app> loads external subtitles automatically if <gui>Load subtitle
+  files when movie is loaded</gui> is enabled in the 
   <link xref="preferences">Preferences</link>.</p>
 
-  <p>To manually load a file with subtitles for a movie:</p>
+  <p>To manually load an external subtitles file for a movie:</p>
   <steps>
     <item>
       <p>Press the menu button in the top-right corner of the window and select