[librsvg] Add an overview to the docs

[Federico Mena Quintero <federico src gnome org>]

commit a0a1147168fca0b3f4b0b872685d6d53796d764e
Author: Federico Mena Quintero <federico gnome org>
Date:   Mon Nov 20 17:00:21 2017 -0600

    Add an overview to the docs

 doc/Makefile.am   |    3 ++-
 doc/overview.xml  |   37 +++++++++++++++++++++++++++++++++++++
 doc/rsvg-docs.xml |    2 ++
 3 files changed, 41 insertions(+), 1 deletions(-)
---
diff --git a/doc/Makefile.am b/doc/Makefile.am
index 5decdda..a2d2ed4 100644
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -95,7 +95,8 @@ HTML_IMAGES =
 
 # Extra SGML files that are included by $(DOC_MAIN_SGML_FILE).
 # e.g. content_files=running.sgml building.sgml changes-2.0.sgml
-content_files = \
+content_files =                \
+       overview.xml    \
        version.xml
 
 # SGML files where gtk-doc abbrevations (#GtkWidget) are expanded
diff --git a/doc/overview.xml b/doc/overview.xml
new file mode 100644
index 0000000..5e7be49
--- /dev/null
+++ b/doc/overview.xml
@@ -0,0 +1,37 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<chapter>
+  <title>Overview of Librsvg's API</title>
+
+  <para>
+    Librsvg's API is divided into two main parts:  one for loading SVG
+    data and one for rendering it.  In the <emphasis>loading
+    stage</emphasis>, you create an RsvgHandle object from SVG data,
+    which can come from a file or from a stream of bytes.  In the
+    <emphasis>rendering stage</emphasis>, you take an RsvgHandle and ask
+    it to render itself to a Cairo context.
+  </para>
+
+  <formalpara>
+    <title>Loading</title>
+
+    <para>
+      RsvgHandle is an object that represents SVG data in memory.
+      Your program creates an RsvgHandle from an SVG file, or from a
+      memory buffer that contains SVG data, or in the most general
+      form, from a GIO stream that will provide SVG data.  At this
+      stage you can get either I/O errors or parsing errors.  If
+      loading completes successfully, the RsvgHandle will be ready for
+      rendering.
+    </para>
+  </formalpara>
+
+  <formalpara>
+    <title>Rendering</title>
+
+    <para>
+      Once you have a loaded RsvgHandle, you can render it to a Cairo
+      context any number of times, or to different Cairo contexts, as
+      needed.
+    </para>
+  </formalpara>
+</chapter>
diff --git a/doc/rsvg-docs.xml b/doc/rsvg-docs.xml
index 1e72a63..12b5051 100644
--- a/doc/rsvg-docs.xml
+++ b/doc/rsvg-docs.xml
@@ -119,6 +119,8 @@
       </itemizedlist>
     </partintro>
 
+    <xi:include href="overview.xml"/>
+
     <xi:include href="xml/rsvg-handle.xml"/>
     <xi:include href="xml/rsvg-gio.xml"/>
     <xi:include href="xml/rsvg-cairo.xml"/>