[gnome-games] coding-style: Add error message rule

[Adrien Plazas <aplazas src gnome org>]

commit 9a1da81f6c38ebb726386f00c0954aa1088795a4
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Tue Jul 26 10:31:13 2016 +0200

    coding-style: Add error message rule
    
    Add a rule explaining how error messages should be formatted.

 CodingStyle.txt |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/CodingStyle.txt b/CodingStyle.txt
index ed9d181..a465279 100644
--- a/CodingStyle.txt
+++ b/CodingStyle.txt
@@ -138,3 +138,9 @@ Vala projects.
  * Any 'else', 'else if', 'catch' block or any other sepcial block
    following another one should start in its own line and not on the
    same as the previous closing brace.
+
+ * Internationalize error messages, which implies using printf style
+   string contruction rather than string templates.
+
+ * Append the original error message to the one you are building when
+   refining an error.