[gtk-doc] docs: mention DISTCHECK_CONFIGURE_FLAGS in the manual

[Stefan Kost <stefkost src gnome org>]

commit af19cf4b8447386d909aff46fb88b3ca64eab243
Author: Stefan Sauer <ensonic users sf net>
Date:   Sun Feb 9 10:55:54 2014 +0100

    docs: mention DISTCHECK_CONFIGURE_FLAGS in the manual
    
    Explain how to ensure that make dist will include prebuild docs.

 help/manual/C/index.docbook |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)
---
diff --git a/help/manual/C/index.docbook b/help/manual/C/index.docbook
index b826ef0..1b88217 100644
--- a/help/manual/C/index.docbook
+++ b/help/manual/C/index.docbook
@@ -494,6 +494,18 @@ AM_CONDITIONAL([ENABLE_GTK_DOC], false)
       </important>
 
       <para>
+        To ensure that a release contains the docuemntation, add this line to
+        Makefile.am:
+        <example><title>Enable gtk-doc when creating a release</title>
+          <programlisting>
+<![CDATA[
+DISTCHECK_CONFIGURE_FLAGS = --enable-gtk-doc
+]]>
+          </programlisting>
+        </example>
+      </para>
+
+      <para>
         Furthermore it is recommended that you have the following line inside
         you <filename>configure.ac</filename> script.
         This allows <application>gtkdocize</application> to automatically copy the