[gtk-doc] tests: add example for include in source-code

[Stefan Sauer <stefkost src gnome org>]

commit 8f451a60b2290863194d137e02e1c5b477293de8
Author: Stefan Sauer <ensonic users sf net>
Date:   Wed Jun 28 22:05:12 2017 +0200

    tests: add example for include in source-code
    
    See https://bugzilla.gnome.org/show_bug.cgi?id=783420

 tests/gobject/src/gobject.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/tests/gobject/src/gobject.c b/tests/gobject/src/gobject.c
index b4f19f2..2a455c1 100644
--- a/tests/gobject/src/gobject.c
+++ b/tests/gobject/src/gobject.c
@@ -32,6 +32,9 @@
  * A new instance can be created using the gtkdoc_object_new() function. The
  * whole lifecycle usualy looks like shown in this example:
  * |[<!-- language="C" -->
+ * #include <glib.h>
+ * #include <glib-object.h>
+ *
  * GObject *myobj;
  *
  * myobj = gtkdoc_object_new();