[gnome-chess] help: Link to an external resource for Chess rules

[Andre Klapper <aklapper src gnome org>]

commit 19ac1d4b93e2c4636ef2de53dc8e8ae45108c5f1
Author: Andre Klapper <a9016009 gmx de>
Date:   Wed Sep 5 10:18:38 2018 +0200

    help: Link to an external resource for Chess rules

 help/C/rules.page | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/help/C/rules.page b/help/C/rules.page
index cc1d3eb..95d9b1c 100644
--- a/help/C/rules.page
+++ b/help/C/rules.page
@@ -16,4 +16,7 @@
 
   <title>Rules</title>
 
+  <p>Please refer to a public book to learn the rules of the game, for example the
+  <link href="https://en.wikibooks.org/wiki/Chess";>Chess book on en.wikibooks.org</link>.</p>
+
 </page>