[gnome-robots/arnaudb/modernize-code] Add a translators explanation.

[Arnaud B. <arnaudb src gnome org>]

commit 6cd77d38bb4e69deca9e1c6379e4723e3c8b33fd
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Sat May 23 22:39:06 2020 +0200

    Add a translators explanation.
    
    See #14.

 data/org.gnome.Robots.appdata.xml.in | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/data/org.gnome.Robots.appdata.xml.in b/data/org.gnome.Robots.appdata.xml.in
index 158ccae..fbfdaaa 100644
--- a/data/org.gnome.Robots.appdata.xml.in
+++ b/data/org.gnome.Robots.appdata.xml.in
@@ -7,6 +7,7 @@
   <name>GNOME Robots</name>
   <summary>Avoid the robots and make them crash into each other</summary>
   <description>
+    <!-- Translators: "It is the distant future: the year 2000" is a reference to Flight of the Conchords, 
see https://www.youtube.com/watch?v=2IPAOxrH7Ro -->
     <p>
       It is the distant future: the year 2000. Evil robots are trying to kill you.
       Avoid the robots or face certain death.