[release-notes] Add Boxes screenshot

[Michael Catanzaro <mcatanzaro src gnome org>]

commit fe1bc7cad1a66c23485127315450d8d9a67a429a
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Thu Sep 3 11:11:43 2020 -0500

    Add Boxes screenshot

 help/C/developers.page | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/help/C/developers.page b/help/C/developers.page
index a0d171ad..8f8daa08 100644
--- a/help/C/developers.page
+++ b/help/C/developers.page
@@ -26,9 +26,9 @@
   <p>GNOME &gnomeversion; includes many new features and improvements for those
   working with GNOME technologies. Read on for more details!</p>
 
-  <section id="boxes">
+  <section>
     <title>Boxes</title>
-    <media its:translate="no" type="image" src="figures/placeholder.png"/>
+    <media its:translate="no" type="image" src="figures/boxes-xml.png"/>
     <p>Boxes is GNOME's application for managing virtual machines and remote
     desktop connections. When creating a new virtual machine, Boxes
     now allows users to manually select the operating system if it fails to do