RFC 0012 : only refers to .duniterkey yaml format

rfc/0012_authentication_file_format_v1.md → rfc/0012_duniterkey_authentication_file_format_v1.md

@@ -9,13 +9,19 @@ Last edited: 2020-02-12
 License: GPL-3
 ```
 
-# Authentication File Format
+# Duniterkey Authentication File Format
 
-This document serves as a reference for a interoperable authentication file format.
+This document serves as a reference for the `.duniterkey` authentication file format.
+
+## Limitations
+
+This format is a container format. Its main caveat is that you can have inside a data not be compatible with your application.
+
+This is the same problem as video containers. The video codec inside the container can be unreadable by your application.
 
 ## File format extension
 
-Cesium client use the ".duniterkey" extension. So for now, the official extension is `.duniterkey`.
+The official extension is `.duniterkey`.
 
 ## Text File Format