doc: Improve "Library" and "Compositors" chapter

Originally written Tiago Vignatti <tiago.vignatti@intel.com>

Some modifications to adjust for previously merged conflicting patches and link
to the sections (instead of <emphasis>).

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

doc/publican/sources/Compositors.xml

@@ -9,6 +9,17 @@
   <para>
     Compositors come in different types, depending on which
     role they play in the overall architecture of the OS.
+    For instance, a
+    <link linkend="sect-Compositors-System-Compositor">system compositor</link>
+    can be used for booting the system, handling multiple user switching, a
+    possible console terminal emulator and so forth. A different compositor, a
+    <link linkend="sect-Compositors-Session-Compositor">session compositor</link>
+    would provide the actual desktop environment. There are many ways for
+    different types of compositors to co-exist.
+  </para>
+  <para>
+    In this section, we introduce three types of Wayland compositors relying
+    on <link linkend="sect-Library-Server">libwayland-server</link>.
   </para>
 
   <section id="sect-Compositors-System-Compositor">
@@ -45,7 +56,7 @@
      </para>
      <para>
       X applications can continue working under a session compositor
-      by means of a root less X server that is activated on demand.
+      by means of a root-less X server that is activated on demand.
      </para>
     <para>
        Possible examples for session compositors include
@@ -75,6 +86,12 @@
 	    rdp session
 	  </para>
 	</listitem>
+	<listitem>
+	  <para>
+	    Weston with X11 or Wayland backend is a session compositor nested
+	    in another session compositor.
+	  </para>
+	</listitem>
 	<listitem>
 	  <para>
 	    fullscreen X session under Wayland

doc/publican/sources/Library.xml

@@ -5,6 +5,23 @@
 ]>
 <chapter id="chap-Library">
   <title>Wayland Library</title>
+
+  <para>
+  The open-source reference implementation of Wayland protocol is split in two
+  C libraries, <link linkend="sect-Library-Server">libwayland-server</link> and
+  <link linkend="sect-Library-Client">libwayland-client</link>. Their main
+  responsibility is to handle the Inter-process communication
+  (<emphasis>IPC</emphasis>) with each other, therefore guaranteeing the
+  protocol objects marshaling and messages synchronization.
+  </para>
+
+  <para>
+  This Chapter describes in detail each library's methods and their helpers,
+  aiming implementors who can use for building Wayland clients and servers;
+  respectively at <xref linkend="sect-Library-Client"/> and
+  <xref linkend="sect-Library-Server"/>.
+  </para>
+
   <xi:include href="WaylandClientAPI.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
   <xi:include href="WaylandServerAPI.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
 </chapter>